I think bundling ’em all together as one would be a good idea. They’re all similar in name, in Direct3D support, and in the fact that they all had a free-form slant to the racing. And yet, all of ’em had different vehicles and different developers.
My loose ranking would probably go…
1. Monster Truck Madness 2 (mainly nostalgia-fueled since I owned it shortly after it came out, but the WCW tie-in was pretty great lol especially the multiplayer rumble modes)
2. Midtown Madness (absolutely no points taken off for the sandbox mode being simplistic, considering this came out in ’99 after all)
3. Motocross Madness 2 (refinement at every angle, and a classic-era Incubus song for the intro)
4. Monster Truck Madness (the debut of the franchise, and also one of the first games to showcase both Direct3D and The Zone)
5. Motocross Madness (I think this was a sleeper hit for me, as it had some great foundations)
6. Midtown Madness 2 (the only game in the series that I couldn’t get with, there was just too much left on the drawing board tbh)