I choose the '08 because I was partial to the design changes both inside and out. I think the center console on the SE & LE trim levels is a significant improvement. I also like how the front is more sloped. It's a subtle change, but I really like the way it looks.
As far as reliability goes, I have been happy so far. I am included in the recall for the fuel sending unit, but it has not been a problem so far. I'm still looking into the radiator bypass. I'm not sure if things were changed from the earlier models or not.
My normal preference is to buy used to save the money like you said, but with the incentives right now, buying used may not be as great a deal as it normally is. Nissan is offering $2500 cash back right now. I bought my '08 new for $26,XXX out the door not including tax and registration. It really didn't save much to buy used and since I liked the changes made in '08 that what we decided to buy.