I'm pretty sure United advise front doors + overwing exits for water landings on their 737s (during the SLF saftety briefing) - I'll be on one tomorrow so I can try to snap a picture of the safety card to verify too (they definitely advise against using the rear doors except when instructed by the crew). I don't think I've ever been on one without rafts, most of their 737s seem to be ETOPS regardless.
Can't remember what they advise on the A320 though, or what other airlines do on theirs.