Whichever one was better maintained... (gasp!) I4 is made for people who wants to just get in the car and drive. It is designed to require minimal maintenance. V6 is for the folks who wants more from a car, and won't mind putting the extra time and money in its maintenance. If the V6 is maintained the way it is supposed to, then no worries. But if the V6 is neglected, it is a bigger liability than the I4. If you don't know the history of the car, the risk is greater. This is for cars with 100K+ miles on them. You mentioned dealers. If you get a CPO with low miles (30K or less), then you get powertrain warranty up to 100K miles. Then you have absolutely nothing to worry about.