Sorry, i have to go against the consensus and say Mech Avids are sooooo 90's. feel, reliability, weight, can't compare to hydro. Yes I've had em both.

I suggest picking up a Hayes HFX-9 Carbon front set, a standard 160mm rotor, and use metallic pads. Strong, cheap, dead reliable. I've used may discs on my commute and this is my preferred setup. Going bigger increases the chance of whacking it on a curb, rack, or something.

my 2cents

Cheers