The new Shimanos are fantastic. Even the new Deores have stacks of one-finger stopping power. Got a set on my Singlespeed, and can't fault them for what they cost.
I've heard really good thing about Hope brakes, supposedly the same stopping power but more modulation. Never used a set though.
As for Avids. I'd avoid them , had nothing but issues with them. They're a pain in the arse to bleed, and have minimal clearance. Don't think I've ever had a set which didn't have a disk rubbing somewhere.
If it was me I'd work out my budget, and then select Deore/SLX/XT accordingly. Having owned a set of XTs and owning a set of Deores, there is very little difference between them. I'd buy another set of either without batting an eyelid.