DEFINITELY 3.5!!!! I had the 3.5 and it just does not compare to the 2.5 (that my best friend had). The take-off is amazing and the gas mileage is not much different. It's a huge power difference and it is worth the extra $ if you want to feel like you are going somewhere when you press the gas. I have driven both and there truly is a difference. At this point, I would never even consider the 2.5....If it is a car you plan on keeping for a while, not just a car to get from point A to point B on a budget, GO WITH THE 3.5, you won't be disappointed...Hope this helps, good luck.