Considering the fact that you don't know which one to choose, I wouldn't choose at all. I mean, do you like them both? If you started a relationship with one but had feelings for the other one at the same time, it probably won't turn out very well, especially if you ended up liking the one you're not dating more. If you like neither, then you should let them know that and stay friends. If you like one of them and just don't want to hurt the other one, well, they both said they're fine with whatever you decide, so then just go with the one you like.

Basically, go with your heart, as cliche as that is, and if you don't know which way to go, wait for it to become clear before making a final decision.