The best? I like Monster 4x4: Masters of Metal best because it has a couple of different types of events, a bunch of real trucks, and a physics engine which allows for 360 degree spins (donuts), wheelstands, and other tricks. Plus there is a lot to destroy, and it just really gives the feeling of the Monster Jam monster truck shows it is based on. Being a monster truck fan, I prefer that, though Rep Fan and others would disagree with me.
Thunder Truck Rally shares the most with MTM 2, it has the circuit and rally modes. Drives the most like MTM 2, but the trucks feel about 2,000 pounds heavier, and they take damage so you can't floor it over jumps like in MTM 2.
Monster Truck Rumble is probably the worst, it just feels/looks/drives cheap. Glad I payed next to nothing for it!
Any other questions, just let me know