If you're only running 1 account, the it's definitely questing, if you run into problems with that, I suggest you switch to grind leveling. Running dungeons is not worth the risk, if the dungeon group doesn't consist only of 5 other or your own bots, then it's too risky. It's much too risky if it gets stuck and that sort.
1. Questing
2. Grind Leveling
3. Dungeoning (Last resort) - Although Dungeoning can be the fastest, if you supervise the bot 75% of the time.