The difference between P90X lean and P90X Classic are:

The Classic is more for muscle building and the cardio workouts are more intense. If you are looking to gain more muscle and be a better athlete than I would recommend the classic version.

The Lean program has a lot less muscle building and more core and yoga workouts. If you are wanting to shed more fat, be more lean or just starting out I would recommend the P90x lean.

When purchasing the P90x program it is important to know that both P90X lean and P90x are included in the program, they will send the videos of both and then you can choose which P90x program will work best for you. Click here to purchase if you have not ordered your p90x program yet

Good Luck!