Get a team with two 55s and four 50s. Put the power hitters in 55 slots to maximize their effects; support and annoyer slots don't need their levels as much and can be kept at 50.

Make sure your Stat Exp. is up high in order to keep up with your opponents' stats, expecially on the 55s which can use all the stats you can give them. There's not much you can do about DVs without fighting hundreds of battles, but if you feel like building up a team to be as strong as they can, it's worth an extra 15-17 points.