I commute via hardtail mtb - wouldn't have it any other way due to the nasty pothole streets with more than the occasional pieces of cars, big city vehicle nuts and bolts that have dropped off - and this one factory I go by everyday that has dropped metal shavings all over (source of 4 flats till I changed up my mtb tires to kevlar).
I do use my other bikes (roadie and FS) on occasion when the hardtail is under the weather though - and I ride more carefully then.