My previous favorite leveling experience was enhance shaman (and is still my hands down favorite dps spec). This was years and years ago. You auto-attacked and shocked until 40. Then after acquiring some buttons to push, began to absolutely decimate anything in your path to lvl cap. The class quests made me feel shamany *cough, bring back class quests* (I'll never forget why you are actually there in org Gamon, old rogues /wink). Then as the changes came I still enjoyed how hybrid the class actually felt. I digress.
Having 3 "forms" and options for play style keeps it fresh. Almost every other class/spec just settles into a leveling rotation for blasting mobs and trucking on. Hmm ill void for a bit and try to make the most out of meta for a while. Or any other summon and make the most of demon hunting glyph. Or back and forth, or zomg full fury pull everything in 100yds and go ape! Regardless, it is fast, efficient, and fun as heck. I feeeeel like a warlock. I feeeeel like a demonology warlock!
Not too sure on what I want from it end game. I probably won't be able to stomach northrend. Except sholazar! I really loathe northrend for some reason. I think I got most of my alts up during wrath.
Thank you dusty demo lock for reinvigorating my passion for this game.