I'm not so familiar with all the latest ones, but I've got a very small project I'm thinking about.
Probably going to run it off of a CR2032.
Timing/clock accuracy not important, whatever built in osc is probably fine. Probably will run it slower to save power using CLKPR, etc.
Must be able to sample 5 buttons, any combination of buttons can be pressed at any given time.
Must be able to light 5 LED's (again any combination can be lit at any given time).
Needs to be able to sleep with as little power consumption as possible (but wake up if any of the 5 buttons are pressed).