I've got a couple grass types! My strongest is definitely my Breloom, and he's both Grass and Fighting type. I've also got a Pokemon who's part Grass, part Ghost, which is really neat.

Though, if you want my opinion, the best types you can get are Electric and Fire. They're both super strong, and Electric doesn't have too many weaknesses, other than Ground.

[Because he's not at all biased with like. ....seven fire types on his roster.]