Well, i'm gonna start with who overall stat wise, is the worste.
Well, he can easily run similar sets to a basic Swampert.
Having access to Earthquake Stone Edge Waterfall Ice punch and Brick Break ( instead of Hammer arm )
So its a very similar movepool. As far as pro's and cons, I would say none of his stats can compare to the all mighty swampert, although he has a nice amount of hp, and some decent physical stats, definetily for NU use, but can also do some good in a trick room team, having 35 base speed.
Well, for standard use this guy is a weaker version of gastrodon, but lets look at where he stands.
He's been pretty useless but really cool looking every since he was introduced ( Pokemon just HAD to put him in the same generation as swampert )
Cons - High HP with weakish defenses, with leftovers and 252 ev's in both defenses, he can take about 2 hits before he's at like 5 hp left. Horrible offensive stats, and not much speed, his only high stat is hp.
Pros - Mainly one, and that is now with his ability hydration, he can be a resting beast.
Hydration will heal him of his sleep in time for him to attack next turn, and also protects him from toxic, so if EV trained in both defenses, he is actually good enough to rest off his blows, while setting up D-dances, and eventually sweeping!
If your not in rain, this guy is like an improved Whiscash.
But is not near as usefull, if he hasn't gotten the move tutor move from Hg/SS known as Earth Power.
Comparing to everyone else, Gastrodon is actually my most reccomended for NU battling.
Cons - Not the most amazing defenses, but decent, horrible speed, and only decent attacking stats.
and a very limited move pool
Pros - Really Nice Hp, better attacking stats that his NU competitors.
I haven't liked this guy since he was released.
But I'll be fair because he isn't that bad.
Cons - Still not amazing defenses and both attacking stats are equal at 85, more speed than others, but that speed was taken away from the more important things he needed, seeming as they didn't give him enough to do anything either way.
This stupid thing CAN'T LEARN WATERFALL.
Pros - In comparison to his fellow Water/Ground types, he is the fastest, and the most balanced, although his balanced stats are balanced at a low, I do not reccomend this pokemon.
By far the best Water/Ground type.
Cons - Speed, thats IT.
Pros - Above Average Attack of 110, wide movepool, nice defenses balaced at 90 great hp, and even usable Sp attack at 85, meaning he can even be used as an ingame surfer, this thing has the highest overall stats of the water/ground type pokemon, and the best movepool. Best dealed out stats, and is by far the best of the group.