My way of the priest: Fuck what everyone else says

So everyone says you have to go shadow to solo a priest, and that you have to go holy to do good in instances. Everyone says spirit sucks. They're all wrong.
At lvl 50 my priest is full discipline +5 in improved renew and +5 in spirit tap with about 90 base stamina, 140 base intellect, and 301 base spirit (+29 with my own buff), and it's great. When I'm soloing and I kill something, I just wait 15 seconds (spirit tap gives 15 seconds of double spirit after a kill) and most of the mana I used is back. In instances, I can keep two people renewed indefinately and if more is required, my mana still lasts a long time. I regen 97 mana per tick normal and 15 while casting (That's 538 mana between pairs of renews). Except for rebuffs and boss fights, I hardly ever need to drink in an instance.

Could I be more efficient at healing or soloing? Probably, but this spec is very good for both, which is really what you want allong the road to end game.