I have an x-mart MTB. I got it for $5.00 from the city impound. I put on new brake pads, cables and tubes. After lubing up the chain, it was good to go. I have since added a rack and upgraded the crankset, but otherwise, it's still the lowly bike with some sort of criminal history that called to me from a pile of other bikes.

I commute on a 20+ year-old road bike, but for what little off-roading I do, this has served me well.