First char was mage in Vanilla, really enjoy the caster classes. After getting him to 60 and playing around a bit started on other classes, soon as I levelled a warlock I was in love and that char has remained my main ever since. Levelled all the classes at some point and like to play around with them, especially as things change and to see what each is like but my lock is always to go-to char, the first one levelled each xpac and the one I focus most of my effort on, don't think that will ever change.
Rep has never bothered me that much, my main is the one I try and get all of them to exalted, but I grind certain reps on other chars depending on how I feel that xpac, sometimes just to get patterns for certain profs since I've maxed them all out across different chars, and sometimes just because certain reps feel right for certain alts (such as wanting Aldor and similiar reps at max for my Draenei Paladin).