OK then I would say, buy whichever one feels better when you ride it (Ride it as far as they'll let you, take it out in the parking lot, go around the building, etc). I think if the prices are similar, and they're both at the same store, the quality is unlikely to be significantly different between the two. I agree that if you start having problems, taking it to an actual bike store for service is the way to go, but most likely you'll be happy with it for occasional riding.
And, if you really get seriously into biking, your first bike purchase will not be what you finally decide you want no matter WHAT you buy
. So don't worry about it.
[edit] Oh and it's probably going to come with big ol' knobby tires. If you really spend most of your time riding on trails, that's fine, but if you're like most folks and only occasionally hit the trails (most of your riding is around the neighborhood, to school, etc) go to a bike store and buy the cheapest SMOOTH tires that'll fit your bike. They probably won't be totally smooth, but they'll be a lot better than the knobby ones your bike will come with. I got a set for my son's bike for like $15 for the pair. If they don't have really cheap ones in stock, ask them to check their catalog. You should be able to get a pair for like $20 or less. Smooth tires will let you go faster, ride smoother, etc.