I ride with SPDs and clipping out is second nature now. I do not have to think about it, and it is nearly instantaneous. You can not beat clipless pedals for XC style riding and efficiency.

I have a pair of the lower end shimano SPDs (might be the 520s), and a junk pair of Nashbar knockoffs. Both work fine, though the nashbar pedal's bearings do not feel too good after a couple years of abuse. Bicycling magazine gave teh Performance brand SPD pedals a good review a couple of months ago.

Enjoy your ride