Just choose whatever color or style you want for your Poliwag when it becomes a fully evolved fighter. Politoed is used usually for special attacking and Poliwrath is used for physical smashing. I know it's hard to choose which one looks cooler because I have the same problem with FFXI (tanking, damage-dealing, thieving, ranging, healing, nuking etc.). Just choose which ever evolution you desire. It's up to you. But remember, once your Poliwag is fully evolved, you can't change him / her back again.