I have been playing as a priest for 5 years now, and mostly as a healer. I would without doubt recomend discipline, since I find it much more fun, the aspect of the game that you actually react before something happends is how I prefer to play. But on the other hand, I do not know if you want to just get by healing or actually would like to play as a healer. I usually recomend holy for starters tough, I find it easier, considering it's much more forgiving than discipline (don't get me wrong here, just my personal opinion). I mean, currently my shields is the healing and atonement because of it's fast nature it just outheal others.
I mean, if played correctly you can just outshine others, like:
http://www.worldoflogs.com/reports/r.../?s=991&e=1381
To be fair to my guildmates, I did not fly, I didnt pick up a single feather at all, on the other hand, I didn't pick up the damage buff either.
But if you are going for the easy solution, I think holy is the way for you, it's more forgiving. Instead of preshielding the raid before a heavy damage taken income, you can just use Divine Hymn while or after the damage occoured. And for some reason people like to feel stronger, and holy without doubt got a lot more healing numbers and higher numbers than discipline. First time I went holy this patch, I felt I had to pass 200-300k hps, compared to the healing numbers from discipline.
Anyway, I recomend Discipline since that's what I enjoy the most, with great results.
-Tobbx