jellicent is a unique water type because of its ghost typing, which gives it access to tools such as will o wisp, immunities to normal/fighting, and taunt. it has access to reliable recovery, enough special bulk to invest fully in its physical bulk, and enough speed to outspeed other walls. it also has enough of a wally reputation to maybe pull off a surprise offensive set (scarf water spout anyone?). however, that ghost typing that gives it uniqueness is also a curse, because its heaivy susceptible to knock off, which it does not appreciate. it can be worn down by toxic, entry hazards, and can't always switch in repeatedly.
a newcomer to the scene, primarina mainly checks in to this list as a nuke. its main selling point is a 126 special attack stat, which lets it destroy a lot of pokemon when holding a choice specs with its dual stab attacks + ice beam. it also can run bulky variants, especially with its 116 special defense stat and its beneficial additional fairy typing, but i would forego that path because it can be outclassed by other bulky waters (some who will appear later).
Seismitoad has a couple of things going for it. it's a good water type switch in, can set up rocks, and is nice for forcing some switches and either fishing for burns with scald or using knock off. its water/ground typing is nice, and it got the edge over gastrodon because of its bigger offensive presence and its better ability to support the team overall, while gastrodon mainly helps itself. the pokemon's still super ugly though.
recommended set:
stealth rock
scald
earthquake
knock off/toxic
ok so hello you dont remember me but i made a list about 500 years ago about the 20 best water pokemon and it sucked big time. so i came back to rectify it (for no real reason, im bored ok). this time i'll try to give better explanations on why each one is ranked where it is. first let me specify some rules:
1. legendary pokemon are not included on this list. this includes the likes of tapu fini, kyogre, keldeo, manaphy, suicune, and palkia; all pokemon who would easily qualify for this list otherwise.
2. im ranking these mons based on how good they are in battling
3. megas are not considered for this ranking either. includes blastoise, sharpedo, etc.
now heres some honorable mentions
-politoed: it has really fallen from grace since its ubiquity in black and white, but drizzle is still enough of a unique ability to qualify it for this list, even though pelipper exists now and outclasses it in recovery, physical bulk, typing, and pivoting.
-blastoise: despite being loved, blastoise has never really been that solid in competitive play. it finds its niche in being a standard bulky water who can rapid spin. other cool things it has going for it is phazing in roar, and preventing itself from being worn down by toxic with refresh.
-quagsire: it's still a nice pokemon for stall, but usually nowadays it'll be passed up as a bulky water by toxapex and as an unaware wall by clefable.
-qwilfish: has surprising tools to make it an effective suicide lead, which is pretty neat. spikes, toxic spikes, taunt, destiny bond, and a usable attack stat keep this thing from being very bad.
-lanturn: one of my favorites, it has nice tools such as t-wave and heal bell in its disposal, and being an water type immune to electric and having to ability to slowly volt switch around makes it pretty nice. it is let down by its very low stats minus hp and it not having good recovery
-gastrodon: just barely missed the cut. it's a nice stall pokemon, and the water/ground typing always lets it breathe easier. another interesting note: arguably the best kyogre check in the game. it doesn't make the list because of its lack of serious offensive presence, and it not having much versatility.
Number 18: Jellicent
Number 19: Primarina
Number 20: Seismitoad