I would say
1. Bulbmin--technically part of the Pikmin Family, immune to all pikmin elements, allows you to not waste other pikmin into candypop buds, however, not usually found and used a lot but so what?
2. White-They are swift, they are untouchable to poison(which is really good for poison walls), they have ground X-ray vision, they are quick at carrying, and they can poison enemies when eaten(although, I try not to make that happen)
3.Purple-sure they are overpowered and can stun enemies but they are weak to ALL hazards in the game and are real slowpokes in carrying back enemies and treasures
4. Red-they are very strong at attacking and immune to fire (great against the fiery bulblax)
5. Yellow- they are high fliers that can reach high places, They can break down electric gates, technically electricity is the most dangerous of the pikmin elements( not counting explosions or boulders/crushing cuz pikmin are not immune to those)
6. Blue-the weakest at fighting, immune to water(appears to be the most common but half of the time the water gets drained out)
So those are my opinions on my favorite pikmin.