Rayman or Crash.

Sonic is a pretty poor series IMO.

Rayman Legends on Wii U is one of the best games I've ever played, period.  Probably *the* best platformer.

DKC regardless of how many overweight Italian plumbers are thrown into the mix.

Ratchet and Clank

DKC series for me, but from an industry impact POV probably Sonic.

Ok, full disclosure, I'm biased out the ying yang when it comes to this question.

I could sit here and do my usual analytical thing and try to give a rational answer and blah blah...

But...SCREW THAT KIRBY IS AWESOME!

In all honesty, Kirby is one of the most fun franchises I have ever played and was my favorite or second favorite franchise on the SNES.

The issue here is that many of the series are pulled down by lackluster entries... I mean first 3 Crash games, are amazing, some of my favourite games ever however, after the PS1, they kind suck. Jak and Daxter 1 is superb, the others are weird open world things and not like 1 at all, so not very good.

Based on the quality of games in the series, how I enjoyed them and all that, the best platformer (outside of Mario) ever made is:

Ristar.

Crash Bandicoot, then Rayman.

Rayman Origins & Legends are the best 2d platformers of the last 20 years.

Mega Man

Dont mean to sound like an asshole but the obvious result was obvious.
Oh no Mario, 90% of the Mario votes end up with DK anyway