Barista AU definitely because Star/Fan AU can be a little awkward/uncomfortable as it’s too close to reality sometimes. That trope needs a very skilled writer like @worryinglyinnocent to do it justice. With Friendship and Fandoms Worry basically did friends to lovers and I adore that fic so much for that. I never got an icky feeling from it, F&F was amazing and Star Force is an absolute gift.
Plus Barista AU has so many twists because it’s quite open-ended. One of them needs to work at the coffee shop/bistro but the other person can do absolutely anything. That could lead to the Barista getting their dream job and so be a stepping stone to a different trope. Basically I think Barista AU has a lot of potential and can go in lots of directions. It’s a starting point, not an end.