Any race in either alignment will make a fine priest.
In order to not get bored with your character, don't worry about what will be "best" because anything can be the best choice if it suits you.
Just choose a race that you think you will enjoy and make that. You're never going to get involved with a toon if you pick it just because someone told you it was the "right" choice. To become immersed in the character, to want to log on and play him till lvl 70 and beyond, you will first have to like him.
It is the sense of involvement... the immersion that will keep you logging on night after night.
I know of a troll warden (defensive druid priest), who is not only a respected healer but also a terrific role player. He's always speaking in character and talking about how "halfies taste gud". (You can read his posts on the SOE warden boards.
The bottom line is that Sony created a very balanced game here and this allows us to be whatever we like without sacrificing playability.