The dungeon and/or pvp route have the advantage of not being ganked by higher level players who with gearing are literally impossible to deal with.
PvP would at least limit it to an 85-89 bracket, while leveling... so no 90s, with amazing gear (fresh 90s, in utter shit gear were taking out 10-boxing 89s.... with PvP gear now, 90s can be horrible for you on a PvP realm).

If you don't level via quests, you can quest later at 90th and make a lot more gold in the process.

If you're on a PvE realm, either approach is going to work.
Do whatever is the most fun.