ALT Coins is nothing but combination of two words, "Alternative" + "Coins". As per layman terminology and thinking, Crypto Currencies are nothing but Bitcoin, but that is not the case, there are many other currencies trading in exchanges and together all are termed as Alternative Coins i.e. ALTCOINS.
Bitcoin has surged nearly 99,577% as on 2nd January 2018, and price of USD 13,363.49 in the past five years and achieving same returns by investing in only currency i.e. Bitcoin is not possible as per my personal views:

Thus, the most favorable or economical way to invest would be invest in altcoins, recently in the past 12 months there has been a huge increase in valuation of altcoins, we can look at the increase of various altcoins:
Ripple – Return of 34,037% in past one year

Ethereum : Return of 8969% in the past 12 months

Cardano

As on, 2nd January 2017, there are more than 2500 currencies which are trading in different crypto exchanges (List of crypto exchanges provided below).
Investing in ALTCOINS can be done in 3 ways:

1. Invest in ICO’s directly:

DEFINITION of 'Initial Coin Offering (ICO)' An unregulated means by which funds are raised for a new cryptocurrency venture. An Initial Coin Offering (ICO) is used by startups to bypass the rigorous and regulated capital-raising process required by venture capitalists or banks. (Source – Investopedia).

This is the best way to jump into altcoins at very early stage, but it comes with its own risks also. As you can understand, that ICO is the first issuance of crypto currency for general public who wants to join the venture and be part of it at a very early stage. The pricing of coins is going to be really cheap may be few cents and when these crypto coins are listed on exchanges then they can be traded as well against bitcoin or any other crypto currency depending upon the exchange. The returns in these coins are huge.

Example – UTRUST Coin was issued in ICO at 0.065 cents per coin which was completed in November 2017 and the listing of ICO was on exchanges such as Kucoin, HITBTC and others on 29th December 2017, currently UTK is trading at 0.54 USD per Coin i.e. a return of nearly 9 times in a month.

There are various other examples of ICO listing at premium over their issue price and are still steady at high prices. But these returns come with huge risk of losing the money by not listing on the exchanges, projects not completed as per the timelines circulated in white paper, listing below ICO Prices and other reasons which can lose the money of small investors.
Investment in ICO directly needs some technical understanding i.e
 Few ICO’s have a condition that you install their wallet and they will require your wallet address so that they can transfer the coins to your ICO wallet directly. Example CIF Coins which closed on 1st January, I installed their wallet copied the wallet addres and then only I was able to purchase / invest in ICO.
 Few ICO only deal with ERC20 coins thus they will ask you to give your ether wallet address which is easier through myetherwallet and metamask. Example – NAGA Coin which I invested in December 2017, I had to open account in metamask and myetherwallet and provide the address to get my NAGA coins on metamask.
 Maximum number of ICO are not in fiat currency i.e. they will ask you to transfer bitcoin, Ethereum or other alt coins.
As on date there are various ICO’s which are ongoing or upcoming ICOS, you should read the white paper in detail, check the listing date if available and invest in the project, you have to see whether the project or the task they are going to complete with the money you are investing is worth to be invested for.

1. Buying through Exchanges:
   Investing through ICO’S comes with huge risk and huge returns but that is not the way of investing for small investor like me, thus we chose the other ways i.e. investing through exchanges and keeping the altcoins with us for long period of time i.e. till the time they grow multifold.
   List of crypto exchanges are:
   Bitfinex
   Coinone
   Bitstamp
   Poloinex
   Bittrex
   Kraken
   Coinbase
   Hitbtc
   Gemini
   CEX.IO
   ACX
   Bithump
   Korbit
   Quoine
   Binance
   Bitflyer
   Kucoin
   From the above list, I have traded in Binance (https://www.binance.com/?ref=12168830), Kucoin and Hitbtc and from my personal experience, Binance is the best amongst the three exchanges but they don’t have all the new coins which are listed in exchanges. If you want to trade in more coins and new coins which are listing in current period then HITBTC and Kucoin are the exchanges which you should be investing through.
   Investing in ALTCOIN through exchanges is also not tough you need to open an account with other bitcoin buy and sell through fiat currency website, do all the KYC and then transfer money to their account to receive bitcoin. Once you receive bitcoin in their wallet you need to transfer these bitcoins to Binance or any other crypto currency exchange as mentioned above and then you can convert these bitcoins against different altcoins of your choice.
   Currently I am based in Thailand, this is the process I adopt to purchase alt coins:
2. Open account with Coins.co.th, complete KYC and start my investment with daily limit of THB 150000, you can have more limit by doing address verification and have a limit of 600,000 THB per day.
3. Once my account is activated and I receive confirmation about it, I will buy bitcoins by transferring THB to their bank account and provide proof of payment in the upload page.
4. Generally, it takes 2 to 3 hours to confirm the payment and receive bitcoins in my cois.co.th bitcoin wallet, they will send the confirmation of your receipt once the transaction is successful.
5. Now you need to open account in Binance, which as mentioned above my first choice amongst all the crypto currencies exchanges because of their low transaction fees and ease of doing transactions. In Binance up to 2 BTC trading limit there is no KYC to be done, but you want to trade more, I would suggest you to do the KYC and increase your limit to 100 BTC. If you wish to open account in Binance use below link:
   https://www.binance.com/?ref=12168830
6. Now, I need to transfer my bitcoins to Binance website, so I will go to coins.co.th and send bitcoin which comes with fees, there are three types of fees on coins.co.th depending on how fast you want your transaction to be processed, I chose the most economical ones as I am never in hurry and chose not to pay higher fees. Please note that their fees are fixed and is not decided on the amount you send, thus if you are going to do this often, transfer big amount and thus your % fees will be very less.
7. Once, I receive confirmation from Binance that the coins are credited to my account, I would go to their website and convert my bitcoins against alternative coins.
8. You can check your order status in open orders and check your balance in wallet balance.
9. If you wish to sell your altcoins and receive money, you need to convert your altcoins by selling them in Binance against bitcoins, send these bitcoins to coins.co.th and withdraw THB by selling these bitcoins on coins.co.th.
   The above process is same for other crypto exchanges also, very few crypto exchanges are there which will let you invest directly in fiat currency i.e. without deposit of bitcoin or Ethereum. I have come across one such in Thailand i.e. bx.in.th, but their KYC is very strict and unable to complete it since past one month. They do offer depositing fiat currency and buying different altcoins through website directly.
10. Mining ALTCOINS:
    The 3rd and maybe the easiest way to invest in ALTCOINS is mining them through your computers. As a hobby you can start this by investing your computer resources and power, you can earn from as little as 1 or 2 USD per day to a higher amount depending upon the resources you have put in and the websites you are going through. If you invest in your hardware i.e. computer and graphic card to start mining crypto currencies, this investment can pay back in next 18 to 24 months depending up to the power rate in your locality and time you give to this part of mining.
    But if you want to earn big money, mining crypto currency is not a choice I would suggest. Rather than investing in hardware and wait for 18 to 24 months for my investment to come back and profit to start, I would rather buy crypto currency directly through exchanges and wait them to grow and then reap the benefits.
    But still if you are willing to mine cryptocurrencies there are two best websites which will help you in mining crypto currencies:
    Hashflare
    Genesis Mining
    There is one more website where you can spend 5 minutes of your day daily and try your luck by spinning the wheel and receive bitcoins for free, I am not sure about the withdrawal part as personally have not reached the withdrawal limit, as soon as I reach the limit shall update on the withdrawal part also.
    http://btcheat.com/?i=458396
    Conclusion:
    I am not an investment advisor and have not posted this post to recommend or make you buy any altcoins. But personally, I believe I should be a part of crypto revolution. I have personally invested some part of my wealth in this revolution and have strong belief that it will grow multi fold, I invested in ripple at 0.2 USD per coin and now it is trading at 2 USD plus, same way invested in Cardano at 0.1 USD per coin and now it is trading at 0.7 USD plus. There are many such coins which you can invest and wait for at least 12 to 18 months to make them a sizable impact in your wealth. I strongly believe that 2018 is going to be year for crypto currencies and huge wealth creation is going to happen. You should not look at price of bitcoins only to see the generation of wealth but should compare and see how much you have gained in altcoins.
    Feedback and suggestions are welcome and I hope I can improve my post from next time and make it more readable and understandable.