If the Cherokee is a 6 cylinder, go with it. The 4.0L straight 6 Jeep engine is among the finest engines ever made. The Jeep V8 had longevity issues. The Rodeo's have always had a severe rust issue in the frame around the rear wheel well and unless you live in a desert, you will have problems with rust. My best advise would be to take both vehicles to a mechanic you trust and for a couple of dollars, he or she will look at them and give you their expert opinion. Spending a little money on an inspection by your mechanic could save you a lot of money later.