I have 5m coins... How should I spend them?

So, I have 5m coins saved up, wondering how best to spend them tbh

I've got Chopper, Rally Car, Dune Buggy, and HC2 upgraded to 20. Muscle Car and Bus are about 18/20.

The following are around 12/20: EC, HC, Supercar, Racing Truck

The following are around 8/20: Lowrider, Hot Rod, Formula, Monster Truck, Muscle Car, Super Diesel, Rotator, Raider

Which would you upgrade and why? Thanks 🙂