I've got five of these, yes five Saleen S7's. 2 MotorMax's and 3 Hot Wheels. I would break them down as follows:
Both of these S7's are curbsides, i.e. they have no engines whatsoever. There is little if any undercarriage detailing. The MotorMax version is slightly smaller than the Hot Wheels version. Paint, overall is better on the Hot Wheels. Tires, wheels and brakes are better on the Hot Wheels. In my own opinion, the interior is better on the MM.
Where the MM smokes the Hot Wheels is opening features. The Hot Wheels gives you opening doors, and an opening glass hatch over the engine that lets you get a closer look at: Nothing. A simulated carbon fiber plate with a roll bar and an air box. That's it. Gee, thanks Hot Wheels! The MM has opening doors, opening front bonnet, opening back glass hatch, and opening trunk. The engine insert in the MM is still just that, but it has a little more detail than the Hot Wheels version. Overall, I like the MM version much better. I bought 3 of the Hot Wheels because I broke a wheel on the first one I bought, and the Hot Wheels does come in a few colors that I like better than the MM. Here is a group shot below.
Not shown is the Yellow MM I have that I haven't completed yet!