Anyways, to answer your question, just play whatever you want man. Pick a class you enjoy and stick with it. If you play a certain class as a "main" picking that to play as a twink wouldn't hurt as you already have experience with it.
'Fun' is a completely subjective term. Asking for help based on what others view as 'fun' will not get you closer to something you'll enjoy playing, unless you just happen to enjoy the same things as other people. There is a lot of information about each class which you can use to find something fun to play, but you will certainly have to decide for yourself what you find fun. No one will be able to make that decision for you. We can tell you what's more or less viable. What's overpowered. What's incredibly weak.
go for pally, there is simply no better class
atm 2 specs u can play, i prefer ret but holadin is well to
as ret u got realy good dmg, ur heal is well ( to heal up ur mates to ), u got a ae dmg style and bubble is special in low lvl as meele verry strong.
u can dispell rogue poisons, whit the 3sec. speed buff talent ur the movment king on field ( behind droods ) u can root u can stun and whit loh u got best * oh shit * button in game.
i play pally in low lvl now many years and this class got always 1 usefull spec.