1500 is a 1/2 ton, best ride, selection of the V6 and all V8's.
2500 is a 3/4 ton, little harder ride and selection of all V8's and V10, as well as diesel.
3500 used to be only a dually, in the new trucks you can get a 3500 with single rear wheels. These are 1 tons. V10 and diesel. Hardest ride.