Amazon Pay just because I had got around 1600 cashback from it (in 4/5 months), and because my main spendings happen through them. Also idk if it might help with the Amazon Pay card, just using what I like the most.
Cons being can't see the remarks and the upi ids to whom you have paid and no dark mode.
Like the interface of Gpay the most and it also has bharatQR option.
Bhim being the most simple and IMO the best base app for the UPI ecosystem, and can have multiple bank accounts at once.