Right now I'm at a toss up between Holy and Ret. This was my original toon from vanilla (though he's undergone a faction change/race change/name change since then) but was only my main during that time.
I'll say deep down I think I want to go ret since I've never really done it as my main spec in PvE. I played it briefly at the start of Cata but other than that I've either been holy (vanilla, cata) or prot (BC, WotLK).
Only thing keeping me back is I already have a DPS as my main. I also have a DK I plan to level from 85 to 90 sometime down the road and I'll definitely be going DPS as well with him. I don't really get bored of DPS, it's definitely the role I'm best at and enjoy the most. Just don't much like the idea of having 2 DPS plate classes. I'd also like to be able to offer a role other than just DPS to my guild when needed. My guild doesn't really ever use alts for the main run but it still would be nice for 5-man/LFR queues and such.
I don't have a problem with Holy I've just wanted to play Ret for a while but never have for one reason or another (did try really hard to play it during vanilla which..didn't end so well), so deep down I think I really just wanna go Ret, but I'm afraid if I do it'll put me off leveling my DK later, plus I'll feel overly saturated with DPS toons.
It's all up to me though my guild doesn't really care. I asked on vent one night and one guy immediately was like "go Ret" so it's all up to me. lol