Purchase Bitcoin with a Credit Card
This is probably the fastest way to buy Bitcoin. However, it's the most expensive way to buy.

The cheapest way is probably with a bank wire. All exchanges have different fee's and as far as I know, Coinbase.com is the highest. Coinmama.com also has a high fee when purchasing with a credit card.

You may also have credit card fee's as well. And the interest on your credit card too can be high.