Each type of Pikmin have different properties and are plucked in a set order as indicated below. They can pick up and carry items to Olimar, and can also latch onto opponents when thrown, with the exception of Purple Pikmin.
Red Pikmin inflict fire damage
Yellow Pikmin inflict electrical damage and fly in an arc when thrown
Blue Pikmin have highest health
White Pikmin deal poison damage and have high speed
Purple Pikmin move slow but deal high knockback
Olimar uses Winged Pikmin for his Up Special. However, the more Pikmin that are following Olimar, the shorter the distance they'll carry him. In addition to Olimar, you can also play as Alph, one of the explorers in Pikmin 3.