I would use mamewah since there's such a huge community around it but its more difficult to manage / setup for the first time.
Mamewah has a very minimal community now. People have adopted Mala, Atomic, and GameEx instead since all three can do more than mamewah without any hassle. But if you prefer scratching your brain modifying .ini's, go for mamewah.
Otherwise, most people seem just fine with mame32 especially if their cab has a trackball. I wonder though... now that MAME has an ASCII front end built in, how many people use that on their cab?
Mame32 is in no way nice on a cab. Everything about it screams casual user on their multi-use desktop/laptop.
Pick one of the big three I mentioned above, Mala, atomicfe, or gameex. Each has its perks depending on the hardware and other features you want. All take little to no time to learn and look great. A side note, GameEx is shareware and requires money to unlock the full potential.
What does everyone think is the best frontend?
As per your first question...