Right now my two primaries are:
* Final Fantasy III (Android port of the Nintendo DS port of the Famicom [Japanese NES] original.)
* Survivalcraft (like Minecraft PE, except it doesn't suck - I really regret paying for MCPE.)
I also have all the Angry Birds games installed, though I only really play AB Space and AB Star Wars and haven't even done those in a while.
Plus John NES Lite for NES emulation, and SNES9x EX+ for SNES emulation, so I can play Chrono Trigger and Final Fantasy V and whatnot.
I also like Zen Pinball HD, but despite having bought a few extra tables, I like the free one "Sorcerer's Lair" the best.