Inexpensive bike = UN-26. That's already a step up from what that bike probably came with originally. That nylon thing that everybody calls a "cup" is really just a bushing that keeps the cartridge from tipping inside of the bottom bracket shell. I've yet to see one have any kind of problem.

Crank sets and bottom bracket interfaces are evolving faster than I'm able to grasp. No way would I try to predict what I might want on some future bike.