I've used Deore RDs for years and have never had a reason to even try anything else. Mud sleet snow, they shift for me every time. Easy to adjust and stay adjusted very well. Very tough, too. And if you do manage to kill one, then chuck it and cough up 25 bucks for another.
I use mine with SRAM Rocket twisters and along with a sram cassette (8spd) and chain I couldn't even imagine a more reliable divetrain.
My friend runs all X7 (9spd) and his stuff runs *almost* as good as mine.