I still prefer to run outside, although we rarely have 6" of snow outside, and I would be inclined to use an indoor track if large enough (5 loops to a mile, for example, which are scarce). Most indoor tracks require 10 loops to a mile, which can strain the knee facing the inside of the track. Alternating directions is typically not possible... Between a small track and a treadmill, I would prefer the latter, but it I find it boring and keep looking at the clock. In most gyms, you need to keep it at 30 minutes.