Glad you’re considering using these technologies for your application! These two payment systems offer different value propositions. If you’re looking for a simpler solution, it would likely be best to just use XRP ledger transactions. Interledger’s value begins to shine when you want to give your users optionality on the currency they want to use. For example, if you had one user that wanted to use XRP but another that wished to use USD then interledger would be a better choice.
The interledger community is actively developing settlement engines for new currencies. Today on the network we have BTC, ETH, XRP, and USD. We’re constantly expanding the set of currencies that interoperate so you can expect more to be added soon.
From my perspective, if you are developing the MVP of your application it might be best to use XRP transactions and just design a clean abstraction so that you could later swap out your payment system if you feel that would provide value to your users.
Let me know if you have any other questions!