Priest healing spec for leveling?

Hi,

Currently im leveling my priest and am just passing level 40, I have specd holy the whole time i've been leveling and have mainly been doing dungeons. Is disc better than holy for my situation? I plan to stay a healer end-game. I have searched but can't find the answers i'm looking for.

Also, since I have been specd holy. If disc is better then am I better of staying holy as I know all the spells, etc or am I better of going disc and learning?

I have got my dual talents, just not sure what to do.....

Thanks in advance.