Crobat is amazing. It is very quick and hits hard. It can take enough hits to stay in as well.
Try and get a nature like: Adamant, Jolly or Lonely.
I never raised a Zubat before; but it hasn't let me down yet.
Flygon is good too; I have one; but it isn't a flying type ha ha. <3
Skarmory is good too; but I get a bit bored of them myself.