I have a 60 Druid and a 34 Druid, I find Druid is the most fun class to level by a long way. It isn't the quickest, but to be honest I have never found a significant difference between any of the classes. HOWEVER, levelling speed can be heavily dependant on spec!
A restoration spec Druid would take longer to level, For levelling you can't beat Feral. It's one of the few specs in game that is equally at home taking on a same level elite, or farming low yellow / green cons mobs.
Mulgore (the Tauren starting zone) is also my favourite starting zone

As for taking time off, you may lose the PvP ranks, but at least Blizzard had the sense to change the system to allow you to continue losing the kit. Doesn't make a huge difference.
If you had PvE kit, then it isn't worse having taken a break (may change once the level increase comes with the add-on though), it is still good enough for everything it was good enough for before. I can point to a couple of times when that certainly wasn't true for DAOC.
MLs may only take 1-2 hours now, but there was over 12 months of ToA (longer than WoW has so far been around...) where it took significantly longer, and exluded all but the most dedicated. They also had a far larger impact on the rest of the game for those that were missing them.