The white one is interesting because you can take both Cleansing Rain and Healing Stream, so it could be a support/healer type pet for an all-aquatic team. Red can have Spiked Skin plus a heal, but it seems like Crawdad does that job better. Blue can have Pump plus a heal, but Purple Puffer does that job better; and Wild Magic is kind of wasted since he has no multi-hit attacks or DoTs. Green can have Whirlpool plus a heal, but again Purple Puffer does that job better, or a crab. Green also has Invisibility, which is a unique ability: the tooltip makes it sound pretty weak, but depending on how the debuff times out, it might actually be interesting (ie DoTs that say they last 1 round actually last til end of current round, plus 1, so it's possible you'd get 2 rounds of attack immunity).