Well, I have both models. The 4th gen V6 has a timing chain and no distributer or rotor. I was concerned about the reliability on the new 4.0 V6, but I have been impressed by the engine. The 4th has better seats, I get slightly better mileage on the 4th gen overall. On the highway, the 3rd gen may beat in mileage, but overall I get about .5 better on the 4th. Sitting in the back on the 3rd is slighlty better, but there is no air conditioning in the rear, the 4th has a vent for air in the back.
I like them both, but as far as the fun factor, I would give the 3rd gen the nod. For crusing on the highway, you will notice a jump in the 4th power over the 3.4 V6.