I am pretty new to this.
I have leveled a priest to early 20s..thats it.
Holy priest has excellent survivability but the damage is not so high.
Shadow priest has better damage but the survivability is not good as holy priest.
But one thing I did notice is that I do not need the uber survivability/tankieness for completing quests (atleast at my level) so should i just spec to Shadow ?
Which spec shines better for ease of leveling ?
The subclass you should play is the one you enjoy more. Nobody else but you can decide which one you prefer to play or where your priorities lie.
It's quite easy to switch subclasses, especially at the lower levels (when it costs a lot less to reset your talent points and you don't have as much invested in your gear.) Therefore, you can easily try one subclass for awhile, figure it out a bit, and if you decide that you don't like it, switch.
Afaik Holy is higher burst damage, so it should work better for leveling (and as you noted, better survivability). Shadow has lots of dots which is superior in longer fights (like elders), but less suited for leveling. Although the difference should be marginal, so in the end like Zazie said go for whichever theme you enjoy more
I play a priest and I perfer Holy as DawnFire said, they do burst more damage than shadow. I am too new at this game but I learned in the past from other MMOs such as this.. with Priests.. I"m Experience player with such class.
when you use only 3 feat on your weapon, holy priest actually have higher damage output than shadow, because holy bolt is one of the feat with highest damage in the game, when you start using socket that's where shadow priest damage start to feel better since holy priest only have 3 offensive feat (may be 4 with judgement but since both subclass have it i didn't count it) . Holy priest also have return and chance to trigger aoe holy damage which is good for fighting a group of mob