Rayman Legends is my all time favorite.
Contra games were great back in the day, albeit a bit frustrating.
Are games like Contra and Megaman considered platformers? For me, it's broken down a bit like this.. a traditional 2D platformer would concentrate mainly on the running/jumping mechanic both for traversal and attack. Some projectile use but not really the main mecanic. So in this case Mario (and maybe like Pitfall) and immediate descendants is the definitive platformer. Megaman, Contra (for me) fall under run'n'gun games, which are a subset of platformer. Mind you, there was a time when these games (well, specifically Contra and Gunstar Heroes and such) were more likened to shooters like Gradius and so forth (since shooting a weapon is the main attack mechanic). Megaman would then fall somewhere in between, tipping more toward the Mario Platform gameplay side of things. Then you have games like Castlevania, Shinobi, Rolling Thunder, Legendary Axe - again, all feature heavy platforming elements, but they feel a lot more in line as "slower run'n'guns" (walk'n'guns?) with purposefully more plodding gameplay.
So, it is difficult for me to narrow it down. Overall I'll always default to the original Super Mario Bros, not only because it is really where the modern 2D platformer really found it's definition, but because it is so stripped down and simple compared to all that was to follow, it the perfect example of a 3D platformer distilled to perfection basically between physics, rules, pacing, rhythm, etc. Lacks a lot of the fancy hoo-yeah which probably keeps it from "best" in most people's eyes, but then I am one for purity and simplicity of gameplay in such a case, timelessness.
It's taken me a long while to concede this, but I have to give the crown to Contra NES however (again, depending on how we are categorizing things). Yes, I said it's a run'n'gun and to me that is different than a platformer, but for most reading this thread I assume they would consider this the same genre. So then, why do I choose this game? Again, purity, simplicity, timelessness. In many ways it feels like a grand evolution of many concepts established in Mario, and enough of a different riff to prevent the two from being confused with one another. Contra looks like it's got a fair amount of advancement in the tech used to develop the game, and the hindsight with which the levels are designed (CLEARLY Mario was an influence). It's not so advanced that it feels like a whole generational increment, but definitely a good amount down the road from it's influences within that same generation. But for me the gameplay, variety, presentation etc all add up to a more satisfying (and evergreen) experience. I can still pick up both games today and have a great time, but Contra I'll more easily lose myself in. The sequels are solid and memorable, but I really feel like they nailed it perfectly enough the first time (also, nostalgia is a helluva drug etc etc). Interested to hear what others have to say on this topic.