Mario most gens. The new games may not necessarily be better than the older ones, but they almost always take advantage of the new hardware in a great way.
Zelda most gens as well. But I don't count BOTW because it is also on the Wii U.
Metroid. Super, Prime 1, and Prime 3 are all fantastic showcases for their systems.
Smash. Each new game is a great expansion on the last with new modes and great new additions to the cast.
Final Fantasy until the HD era.
DK64. Went to far.
Banjo Kazooie nuts and bolts
And the absolute worst is Mobile Suit Gundam Crosswire for the PS3.