At level 19 the best twinks are Rogues, Hunters and Warriors. I've seen people try other classes but at that level you don't have anywhere near enough abilities to be able to do anything against the stronger twink classes. At 29 everything can change, Mages, Warlock ect all start to be come a stronger class and are able to twink although still not a popular choice. But don't forget twinking isn't limited to just these brackets, Everytime someone will decide to make a twink in one of the high brackets as it's more fun with more spells and abilities especially if your one of the classes that dosn't gain alot until your into your 20's.