For XP off BG's:
19's are pretty active with 2 to 5 minute wait times. Games are fairly fun, though some of the players on both sides can be major a-holes, especially to undergeared players. I have 3 level 19 twinks and can play it just about any time I want. Level 19 hunters, pallies and rogues are frowned upon because they are considered OP. Especially hunters.
I have a 59 twink and that bracket is totally dead, although there is a wow forum movement to resurrect it.
I hear tell that the 70 bracket is almost as active as the 19's and the 39's are gaining strength.
Understand that brackets are now split in half. So 10-15's play in a sub bracket away from 16 to 19's. Therefore, level 10 and 15 twinks are actually viable. A new Free To PLay bracket (Blizzard is letting trial account go forever and to level 20 now) at 20 is lumped in with 20 to 24's and that bracket is getting very active very fast. So, you could twink at 20 if you wanted, although 24 is frowned upon.
Thats my 2 cents. Others may have more to say, but this kind of post happens a couple times a week and people may ignore it or flame you. Good luck and please roll horde. Don't forget, you can faction and race change anything but a DK below 60.
