Got my 2008 Colorado last September. Driven 12000 miles. Gas mileage runs 20- 22 in town. Roomy cab, and back seat leg room is adequate for its size. Why the Colorado and not the Silverado? I don't pull anything, and only haul lighter cargo- plus I like the extra room in my garage. I do haul my scooter, and I've carried a bed full of pavers plus three adults with the A/C on and the little 4-cyl powered us right down the road. Engine torques up real quick. Passing on the highway winds it up a little more than I like, but it gets moving right away.
OnStar! (Safest way to drive & talk.) Torque. Reliability. Roomy crew cab for its size. Paint/Trim/Finish. Gas mileage.
We used to call it 'passing gear' - it winds up pretty high when overtaking another vehicle or sometimes when entering a highway, but that's just the 4-cyl engine, and I'd rather save gas!