Crobat and Gliscor are exelent Flying types for Black 2.Crobat having a base stat total of 535 it surely worth its training.Good moveset and with 4 resistances and 1 immunity it is a very good choice.
Gliscor having a base of 510 with Defense the highest stat he could be your wall.It's moveset is good, you can do anything with it.He has 2 immunities,3 resistances and 1 *4 weakness.
Personaly I would go with Crobat.Since Gliscor can't learn Fly and with Crobat having a good attack, it's an advantage.
PS : Posting your team members in B2 would have helped me a lot better