I think this comment by https://www.reddit.com/user/Bingx might answer your question.

"Ripple (Stellar is a fork of Ripple meaning very similar) is based on a classical blockchain that uses PoA (proof of authority). PoA means nodes have to be whitelisted by the company behind Ripple in order to participate. There are advantages and disadvantages to this. Most blockchains are based on either PoW (proof of work) or PoS (proof of stake). One disadvantage (depending on who you ask) of PoA is that because of the whitelisting Ripple isn't decentralized.

IOTA is based on a tangle (DAG) that uses PoW to validate transactions. Tangles are very new technology and IOTA is the largest project (by market cap) that uses a tangle (basically all the coins you see on Coinmarketcap use blockchains). Because the idea of tangle is very new many people (including me) are struggling to completely understand the advantages and disadvantages it brings (but I think we would agree that it is highly fascinating technology). IOTA dates back to 2015 and has been in development since then. One advantage IOTA brings (which until now hasn't been solved in traditional blockchain) is scalability. IOTA scales effortlessly and becomes more secure and faster the more people use it (traditional blockchain can get congested as is happening now to Bitcoin and Ethereum). There are solutions being worked on to scale traditional blockchains (such as Lightning/Raiden) but those solutions have not been deployed as of now and bring their own advantages/disadvantages with them.

An in depth comparison of IOTA vs traditional blockchain could easily fill a small book. A good starting point to learn about the tangle technology on which IOTA is based (IOTA implements a tangle, it is not the tangle) is the tangle whitepaper available here: https://iota.org/IOTA_Whitepaper.pdf"