WHICH ONE IS THE BEST? i heard that theyr all good but i heard that the mercedes has more problems out of the three. Is this true??

First of all, the RX is the worst of the bunch. I had an opportunity to drive the RX along side of the ML, MDX, X5, XC90 under very difficult situations, such as emergency lane changes, and panic manuevers. The RX failed miserably compared to the rest i mentioned, and i must mention that i HATE volvo, but still picked it over the lexus. The best of the bunch was the BMW x5, but since you didn't mention it, i suggest the mercedes ML.