Even though the question is clearly about the "most fun caster" and wizard can probably not fit into that description, I still think you guys are unfair to the wizard class hehe.
First, let's debunk a myth that is 100% forumquest and 0% real p99: wizards can group absolutely no problem, nobody "shuns" on you for being a wizard. Only assholes do that, and the server has a few, and you will lose a spot in a group every now and then I guess. But to say you can't group is simply not true. And wizards in groups are not so bad if you actually try to be relevent, using all the spells you have to make a difference
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Secondly, with Jboots, Teleportation is just super fun. Come on. Wizards having Enduring Breath, Levitate, Invis, Teleports and Jboots, and maybe also Hide if you play a Dark Elf (and really why not play a Dark Elf!?) you are kings of travelling
[You must be logged in to view images. Log in or Register.] and travelling is fun! also, with Stun, Snare, Root and even god forbid Yonder, you can also survive an encounter more than what you get credit for. And with the best DD in the game, with a small GCD reseter, you can usually also burn down a mob using all your mana bar, which is also convenient when travelling (not so much when XPing).
All in all my point is, the question is only about "fun", and not about power, and I think if moving around, travelling and adventuring is your idea of fun, Wizards are definitely a fair option and shouldn't be frown down that much hehe.