I definitely agree with RDN's taste. I'm personally partial to 4th gens because that's all I can afford (and I've never driven a 5th).
Don't worry about the back seats. Love the fact that the 4th gen back seats are like deep storage buckets and nobody wants to sit back there anyway. You don't have to be anyone's chauffer (sp?). The interior is nice and cozy. The function of the two rear seatbelts is simply to keep the insurance down (two-seaters have higher insurance).
Also, the 4th gen is like 200-300 lbs lighter.
Dan