Raichu. Leaving all anime-related sentiment aside, they both have great designs. Pikachu is freaking cute, but for some reason I always thought the concept of Raichu using its tail as a ground to avoid shocking itself was really clever. So it's a tie on design.
As for who would win a battle, Raichu hands-down. It's all really a contest between the weak one and the strong one. You can bet the strong one is gonna win. Raichu, simply put, is harder, better, faster, and stronger (Daft Punk FTW) than cute little Pikachu.