My 2 cents, take with a large grain of salt as I am not as experienced or knowledgeable as most people here...

Pass on the NEXT as they are just kind of crummy. Heavy, made for off-road, some of the parts can be iffy. Can be hard to resell too.

The Trek seems like an OK deal, except the fit might be an issue, plus the knobby tires seem kind of pointless for what you're doing.

Not qualified to speak about the Vector. Given that it's a cromoly mountain bike with knobbies, it's probably not the fastest ride around. For $150, mmmm.

Personally I'd do best on the Nomad as long as it fits you OK. It's claimed to be new and looks that way as well. Some of the parts are decent quality for an inexpensive bike, and the fenders are a nice plus. IMO, try to get him down under $200 and I think that is a fair deal.

Again take my opinions with a large grain of salt and trust the more experienced riders here.