The RX's longer wheelbase translates to a smoother ride, particularly noticeable on highways. However, the NX is surprisingly comfortable for its size, and unless you're consistently carrying passengers in the back or hauling cargo, the RX's extra space might be overkill. Fuel economy is better in the NX, expect a few MPG difference in combined city/highway driving. Consider test driving both back-to-back on the same route to compare yourself.