I face a similar dilemma; played a mage in vanilla and I'm now torn between a mage again (might get boring quick), warlock (might make me miss my mage), rogue (might be too popular) and priest (will it get boring?).
One thing for certain is that I'm definitely rolling alliance and starting in elywnn forest. If only just for nostaliga
Like others, I originally played in a top EU guild but between a job, girlfriend, friends and just general life stuff, I won't be able to commit the time required to push for firsts. Definitely keen on casual MC/BWL/AQ/Naxx and PvP progression though.
I actually booted up the private client to Lights Hope last night, going to level each of my chosen classes to 20, I started the warrior last night. It's VERY easy leveling, but very boring thus far.