My favorite season is Smile, though I can't say that for sure since it has a lot of sub-par aspects too.
I can't pick a favorite, since I am a huge sucker for most pinks and yellows.
My favorite Pinks are the stereotypical, too pure, girly and very Pink ones: Nozomi/Miyuki and Tsubomi. Haruharu is also shaping up to be among them.
My yellows include those that most people would call "otaku bait" or whatnot, like Yayoi and Urara, but you can add Alice to that too (and Kirara is shaping up to be a contender).
And I have a special soft spot for the smallest ones, be them Cures or not (Yayoi is also a part of that), so Ako/Aguri/Marine/Himelda/Regina are easily top tier, while my favorite movie character is Niko-chan.
Like I've said, I can't really pick among all the lovely girls.
Oh, that's right, favorite fairies.
I'm a sucker for the girly ones here too, so I like Milk/Candy/Hummy/Sharuru and Pafu very much.
Can't decide whether Royal Candy or Pafu has the best human form.