well, it depends on if you want to use one of them, and the rest of your team. (also if you need it for the pokedex)
now just in general, politoad if a bit better than poliwrath because of the Drizzle ability. if you have a team that has an advantage in battle with the weather, then go for politoad. if you want an attacker, the go for poliwrath. but again, just in general, politoad is better than poliwrath because of the Drizzle ability
Hope I helped!!!