I'm assuming that you'll be checking at least one bag, so your best bet is Southwest because they allow up to a pair of checked bags for no charge. they're generally pretty close to the cheapest, too, which is nice. you can pick your own seat so if you check in online, you'll get a good boarding zone so you can pick a seat you like, and you can move so you won't get stuck next to a screaming baby or an obese person spilling over into your personal space.
Delta has wi-fi onboard to that's really the only good thing any other airline has going for them.