Believe it or not Holy is pretty easy to level (leveled a priest 1-66 as holy so far) You just have to know what you want, do you want to heal instance? If yes, gear for it. Do you want to Solo grind or quest? If yes, GEAR FOR IT. Its all about your gear as a Holy priest. Shadow you can wear whatever you want, youll still dps like mad, Holy takes a bit more thought in choosing your gear. Im speced for LolSmite(been that way since 39) and Ive found I can dps well, but I'm geared for Int and spell crit mostly, since I can heal myself in between attacks. Also with the Surge of light proc I can overcome mana issues, since its free instant smites, though still not totally reliable yet (even with almost 25% crit chance). As for damage well, at 66 I get 880-1k ever 2 sec, toss a SW pain on for 250 every 3 sec, and im doing 600dps round about. Great burst dps, and unlike shadow I can still heal without gimping my dps. Grinding is fast, drop a mob in 6-12 seconds,depending on surge of light procs, and can do 4-5 mobs before oom depending. BUT if I get jumped by more than mob one at a time I'm screwed, since I have no CC, and no kiting abilites like Shadow priests do, they have better survival rates, no exceptions unless your full Disc. Another great thing about my spec, if I want to get into an instances easier, I can heal for them since I have a good healing set, and if the tank is really good, I can smite in between heals, to make up for slightly weaker heals since I'm not really speced for healing. Mob dies a bit faster when a 700+ smite hits them every so often.