#PumpItUp is the most fun in my opinion, because the pads are big and hard to miss, they're arranged in an X so there's a handy place to put your feet (plus it's a lot harder to mix up up & down since they're not next to each other). It also just... I don't know, has dance sequences that are more fun to do, letting you jump and stomp all around on the pads instead of just barely moving your feet so you can hit the correct one in time. My favorite moments playing this type of game are when my feet touch the floor less than 20% of the time, and PIU lets me do that a lot.
It's also by far the most lenient of the the three when it comes to scoring :D
The window for a Perfect is insanely wide, and not only is there no penalty for extraneous inputs, it doesn't check if you start a hold before it told you to, so if you start a hold half a beat early and release it half a beat late you'll get a perfect. It almost feels like cheating to do that, so I generally don't, but it's still fun.