What high quality carrier would you recommend for Detroit? They can go to Cogent, HE, Level3 or one of their competing Telcos. There is nothing wrong with using Cogent/HE for their eyeball network, it gives them cheap connectivity and allows Cogent/HE to balance their traffic ratios Win/Win.
Also to note Google Fiber uses a lot of nLayer/GTT for their eyeball traffic.
I can't really speak for that area. But if I chose out of three you listed, it would be L3.
A close friend of mine spent years managing the network of a smaller ISP in the northeast using both Cogent/HE for their eyeball network, and he was constantly telling me about packet loss issues with Cogent. On the other hand, I haven't seen as many issues with HE as a whole, more localized.
Either way using the cheaper options is a good choice if you want to keep costs low during expansion. Hell, it's probably still better than what I see through TWC.
Meh, I used to use Cogent in the mix of transit providers for hosting services, and it was more than adequate when peering spats weren't going on (in which case we'd dump traffic over to Hurricane Electric or Global Crossing).
Want quality bandwidth? Pay for quality bandwidth. Most people just want their packets delivered, a few extra 10s of milliseconds be damned.
Also to note Google Fiber uses a lot of nLayer/GTT for their eyeball traffic.