I’m going to assume that your running is mostly outside, since you appear to have no preconceived notions about treadmills.
Anyway, after many hundreds of miles on the treadmills at my gym, I must say that for me the most important thing would be durability and robustness, with such niceties as fancy running programs a distant third. Built in fans, cupholders, TV mount are all a plus.
The ones at the gym are solid, and that’s what I like. Considering how light featured they are, compared to ones at sporting goods stores, and considering how expensive commercial models are, I’m afraid to think how flaky the pretty sporting goods store models might be.
Of course, the extra cost might simply be because the machine needs to withstand a hundred hours of use a week, instead of three. Nevertheless, solidity and robustness are my key factors. I typically run ~10mi at a shot on the treadmill, so I would wear out a shaky one in six months.
Post anything you find out from CR about them.
Oh, and one other thing: if you put it in the basement, make sure you measure the highest point your head will ever be off the floor (e.g. full incline in mid stride) and see if your basement ceiling is high enough. It would be a bummer to get your treadmill and find you can’t raise it up much without hitting your head.