There's something to like about every Pikmin type imo so it's kind of hard for me to really choose just one favorite, so instead I'll highlight what I like most about each type.
Red Pikmin the very first type of Pikmin we were ever introduced to. The fiery soldiers with boosted attack and overall just so iconic with their cute pointy noses. When I think about Pikmin, these guys are the first to pop into my mind. Unfortunately they are outclassed in later installments by Purple Pikmin and Rock Pikmin in terms of sheer strength, and fire hazards are not as deadly as they used to be, but I still think these little red troopers are awesome in their own right. Thank you for helping Olimar retrieve the S.S. Dolphin 's main engine at the Impact Site and thus kickstarting his series of adventures (or misadventures, actually lol)
Yellow Pikmin those big ears are very adorable! Useful of course for gaining lots of height when thrown, allowing them to reach far-off goodies. The only Pikmin type in the first game to be able to hold Bomb Rocks, they then were buffed in the second game by being completely resistant to electrical hazards, which is extremely important as other Pikmin types (except Bulbmin) are simply obliterated if they so much as look at electricity funny. In Pikmin 3 and 4, however, electrical hazards have been significantly nerfed and are no longer a huge threat. Yellow Pikmin are excellent diggers. Overall, these guys are really great!
Blue Pikmin ah yes, the only Pikmin type that feels right at home in water and swims laps around the pond all day. Those mouths are actually gills, as strange as that sounds! Blue Pikmin are always at their most useful around water, and did you know? In Pikmin 1 and 2 only, they act as lifeguards and rescue their drowning compatriots! That's pretty cool! However, with the introduction of Winged Pikmin and Ice Pikmin, they're no longer the only Pikmin type that can get across water. Now, their most prominent feature is fighting creatures underwater and retrieving any sunken goodies.
Puffmin not officially a Pikmin type you can control but the idea of your Pikmin becoming infected by spores and actively chasing and attacking the Captains is a really interesting concept that sadly is never explored further upon beyond Pikmin 1 (and in the case of Pikmin 2, the Bulbmin) The Puffmin are essentially zombies, and they look and sound quite scary, too! They remind me of the symbiotic/parasitic relationships found in nature, much like the concept behind Pokémon such as Paras and Parasect.
Purple Pikmin hefty, chonky, super strong yet super slow, these guys are so very, very, VERY busted in Pikmin 2 lol they're also known for their slam attacks which basically stunlocks foes into submission. In Pikmin 2 and 3 they sound just like the other Pikmin types (except Yellow, Rock and Winged) but in Pikmin 4 they were given a lower-pitched voice which is a neat touch. And naturally, these big chubbos were nerfed since their debut, but I think they're still mighty potent, and you can't go wrong with that charming purple color.
White Pikmin immune to poison AND poisonous themselves when eaten by creatures, these little guys use their Venonat-type eyes like sonars to detect buried treasure and dig, dig, dig! White Pikmin are so teeny tiny and adorable, and man do they have a serious case of the ZOOMIES lol they're fantastic for being the fastest Pikmin type. Even in the leaf stage these guys can always keep up with you. And as flowers under the effect of Ultra-Spicy Sprays? They are soooo fast! Perfect for those clutch moments during the sunset countdown when you need to grab some last second goodies. In Pikmin 4, just like the Purple Pikmin, the White Pikmin were given a new voice: super squeaky and super cute!
Bulbmin again, this explores the concept of symbiotic/parasitic relationships in the animal world, plus they are very useful for being immune to all hazards in Pikmin 2. And they're super cute to boot! If only we could keep them!
Rock Pikmin so satisfying when you throw them to shatter crystal walls and formations, and I just LOVE the way these guys sound! When they're doing a task, even when they are being attacked and killed they sound so adorable! They definitely make my favorite Pikmin noises heehee~ these guys are unique in that they're the only Pikmin type incapable of latching on to enemies to inflict continuous damage, but instead rely on that initial impact from being thrown, which is actually quite busted in Pikmin 3. After being thrown, they simply body slam their foes for chip damage. Much like Yellow Pikmin and White Pikmin, Rock Pikmin are fast at digging. Rock Pikmin also can't get crushed if they are above soft ground, so no need to worry about Beady Long Legs stomps or Armored Cannon Larva rolling rocks!
Winged Pikmin I mean, they fly above all creatures, over water, pits and hazards so of course Winged Pikmin are pretty busted too lol but their biggest flaw is that they are abysmal at non-aerial combat, so get ready to lose a few in those real tough fights. But they are pint-sized and squeaky just like White Pikmin so that's bonus points!
Ice Pikmin when they were revealed to be one of the new Pikmin types in Pikmin 4, I knew they would be pretty broken in combat. Essentially, Ice Pikmin are living, breathing Ultra-Bitter Sprays, a feature in Pikmin 2 only and in that game, those sprays can mean the difference between life and death, especially in the postgame caves. Much like Ultra-Bitter Sprays, Ice Pikmin freeze and shatter creatures, turning them into globs of nectar. I first thought that to grow Ice Pikmin in Pikmin 4, you would need a bunch of Blue Pikmin and fuse them with special ice crystals (the raw materials looked like ice) Also, I think it's funny and cute how Ice Pikmin look like a hybrid between Rock Pikmin and Purple Pikmin.
Glow Pikmin that shade of neon green is really appealing. They are immune to all hazards and you can charge them up for a super strong attack which stuns enemies, very useful during the harder night expeditions. I do like that their flower is uniquely shaped like a star rather than the classic flower like the other Pikmin types. Glow Pikmin are pretty much Pikmin 4's version of the Bulbmin just with extra perks. I find Glow Pikmin seeds to be the most useful in caves, when throwing the Glow Pikmin into Candypop Buds to turn them into other Pikmin types rather than having to sacrifice your other types.