You know, if you ever aspire to do the marathon, the higher mileage is a mental builder, NOT a mental killer. It's long, boring, and requires a tremendous amount of patience. Easy and long, very long. The higher mileage teaches you how to train properly too on your easy days, which are the most important days of the week.
Personally, I like 20-40 min. loops, do those 1-2 times, and then branch onto roads (~run to a neighboring town, campus, park). I'll also find grassy areas and do 20-30 min. of a run barefoot (1-3 times/week). Out and back runs aren't bad either, if the scenery is varied and the run stays steady (~doesn't cross too many streets/stop lights). 20+ mile long runs are fun cause you literally run everywhere!