Sonic Rush is a guilty favourite of mine, but it feels too short and unfinished. I'd love a higher res, expanded edition for the 3DS in 2015, its tenth anniversary, but I doubt Sega will do it.
I've barely played the Advance trilogy, I finished the first and played through a good bit of the second, but something about SA3 just kept putting me off, its reputation isn't that great in the fandom.
The problem is that from the screenshots we have of Lost World on the 3DS it looks like it's been built off of the Generations engine. Generations for the 3DS was very short, linear and disappointing, but I'm not getting a Wii U, so I'm stuck with that version.