Generally I have no issue with mp10, but it takes slightly longer to kill mobs and I may have to kill a boss or two.
Currently I'm level 26, and I'm on the quest in Act 2, The black soulstone.
Now this seems to completely dominate my demon hunter/monk, who are well into act 3.
When I leveled my barb I beat normal mode about 2 days after release, and that was the end of it. I never really came back until my friend got it, and powered me to 60.
So I don't really know what the best way of leveling.
I don't really have alot of whats considered leveling gear, but I have alot of decent experience+ kill gear.
I like both, but my main reward is the end game obviously with inferno and having that prize of the ding and having a new rune or spell to play with, basically a new toy.