Normal modes. Seriously, why is the idea of starting with easy stuff so utterly alien to all newbies? Why does this sort of thread keep popping up over and over, why is every new player instantly trying to get into the fastest shiny/time ratio? Not to be the cliched hater, but is this a WoW thing? Gather random groups off of global for normal modes, even if you never get a single drop you'll be getting experience (which is much more important than pixels). You're also %600 more likely to get actual new people or oldies who aren't quitters, lootwhores or whiny babies when you're setting out to a normal mode run.
If you're clinically unable to do normal modes, Vortex, Pillars, Malice and Palace are easily offtankable on HM with terrible gear. Necropolis, Coppice and Abyss don't even need offtank so you can be dps.