I am upgrading my brakes from old as the hills minis and I want some of the new shimano ones, but what is better, deore, slx, xt, saint etc?

I am pretty hefty and like to ride fast, ish.

slx or xt will cover you for 90-odd% of your riding. saint for full on stopping power with slight weight penalty.

Got slx with 180 front 160 rear find they have more "power" and feel than my old mono 4's with 180's front and back. Pads seem to make a difference to. My bro has 160's front and back with the new xt's they look ace, and with the resin pads in they stop you very quickly!!

The difference in performance between SLX and XT seems to be mostly the pads… I like my XT but with hindsight, I'd buy SLX today.

The pads are the same.

I have K18's but I have used a friends XT's and they are amazing, next brake I buy would be XT!

I have just fitted some of the 09 Saints (came with 203mm rotors, probably overkill but I'm not buying new ones!) to my bike and I am very happy with them – already feeling very powerful but controllable too.
Levers also feel really nice compared to my old Juicys.

deore – xt

Very impressed with the Deore's I've had on a couple of bikes now.

Mister P- "The pads are the same"

Not on the sets I've fitted, they're interchangable but the SLX pad was a different compound.