Contest Battle of the fully-evolved frogs!

[The Froakster]

Greninja. Such an awesome Pokémon.

 

[Arc Blader]

Who has the best design?
Greninja by a country mile. Quite honestly the best-designed Water-type starter there is, and I'm saying that as a devoted Swampert/Blastoise fan.

Who would win?
Err... my gut says Poliwrath strictly on the basis of type, but who knows? It's kind of a mishmash.

Who has the coolest typing?
Seismitoad. Water/Ground is simply the best type combination; anyone who disagrees is just being silly. Poliwrath and Greninja are duking it out for runner-up though - both uncommon type combos, both very interesting type combos.

Who do you like best?
Greninja. The best Water starter in a long time, and easily the most unique one. Poliwrath probably comes next, followed by Politoed.

Final Verdict: Greninja. This was never a fair fight. Greninja wins.

 

[The_Ideal_Dragon]

Toxicroak. He has the best typing, and I like his design.
But.....Greninja would almost certainly win in a battle.
That seems to be the common theme, doesn't it? Greninja and Toxicroak?

 

[Sakuraa]

Toxicroak; best poison-type ever.

 

[Poke Trey]

Greninja because Ash-Greninja is a thing and also the games he is just too OP!

 

[PaulTheProtist]

Toxicroak, he certainly has the most creative design out of the options. I like his typing too.

 

[Gaga]

Greninja

 

[Gengarzilla]

Who has the best design?
I do like Toxicroak's design quite a bit, but Greninja is a ninja.
Point goes to Greninja.

Who would win?
Based solely on type, I'd say either Poliwrath or Seismitoad. Greninja's weak to Poliwrath and Toxicroak while Seismitoad beats Toxicroak. Politoed's a non issue by this point, both of the other two have access to Water Absorb.
In a practical battle though, I'd honestly say Seismitoad. Greninja can ruin Poliwrath with Extrasensory, but that would leave the now Psychic type wide open to Toxicroak's Sucker Punch. Seismitoad then beats Toxicroak while using Water Absorb to negate Politoed's big advantage in Drizzle-boosted Water moves before wearing it down with Toxic and Drain Punch, maybe with Grass Knot too.
Point goes to Seismitoad.

Who has the coolest typing?
I'm going with Toxicroak on this. Poison/Fighting stops Fairy types from ruining its day, and all it takes to defend Toxicroak from the usual fast and frail Psychic type is a quick Sucker Punch.
Point goes to Toxicroak.

Who do you like best?
Thanks to Politoed's evil antics, I immediately gravitated towards the underappreciated relative Poliwrath. It might not be something I'd ever use but I do kinda like the ones who get shafted aside. Explains why I prefer Charizard Y over Charizard X.
Point goes to Poliwrath.

Final Verdict:
Poliwrath: 1
Politoed: 0
Toxicroak: 1
Seismitoad: 1
Greninja: 1
...
...
Yes, I played competitively in Gen V. I'll just wing it and choose Toxicroak on the basis of it being the most likely to kill me if I pick someone else.

 

[Guzma]

Gonna be cliche and say Greninja. It's my favorite starter of all time, partly because it's really cool design-wise, and partly because it's a god in competitive play. I love Toxicroak almost as much, though, since Croagunk is one of those Pokemon that always makes me laugh.

I'll just wing it and choose Toxicroak on the basis of it being the most likely to kill me if I pick someone else.

I dunno, Greninja's a ninja, and the purpose of a ninja is to flip out and kill people...