The platformer series that i played are Mario, Kirby, Yoshi and Wario and of them i think the Kirby series is the best one cause its fun, everyone can play it and it has interesting mechanics.
Also kudos to the Donkey Kong Country series! Ive never played it but it seems challenging and fun at the same time!
Its also really fair.
I seriously couldn't tell you which one is "best". I'm not good at deciding things like that. But I will tell you what I think about them.
Wario Land is awesome, of course!
But not counting that...
Mario:
eh... lost its touch
Donkey Kong Country: With the 2 new ones Retro Studios managed make 2 masterpieces in a row. I have nothing negative to say about those 2 games.
Yoshi's Island:
I'm not even going to consider Yoshi's Island to be a series. Yoshi's Island DS and Yoshi's New Island are not worthy to be part of the same series and Yoshi's Island.
Kirby:
They are excellent! Damn near all of them! I just wish there was another game like Kirby 64. Combining all the different abilities was great fun!
Starfy isn't very good at all. Low-level, repetitive challenges and lots of swimming through open spaces. Yoshi's Island DS is a bit of a mess and the new game looks to be much the same. I have only played the first two Kirby games, and they were pretty good. Simple action, but enough variety to them. The Donkey Kong Land series suffered from the low-end technology (zoomed-in perspective, unclear visuals), but was still quite enjoyable. I love the original Super Mario Land, but the Wario Land series is much more sophisticated.