From my experience the Monster Truck is the most versatile for all the levels and easy to use, flip and land. Also has a lot of power. But certain vehicles just do better on different terrain. The race car, for example, fully built, is great on the highway level. Just do yourself a favor and don't judge the vehicle based on it's level 1, non-upgraded drive ability. All of the vehicles feel very different after money has been put into them (whether it be for better or worse).
WHOA! Definitely the motocross bike. It's so much easier to control and that comes in handy when you're taking jumps. The race car is too long so when you get caught in ditches It's easy to tip the car. The monster truck is too big to even be reliable or useful. The weight completely distorts the chances of going up steep inclines. I'm pretty addicted to this game... As you can see. But motocross bike all the way!
Definitely the 6 wheeler truck. I have the race car, monster truck, and truck all fully upgraded, and to me the truck is best. The race car gets stuck in valleys and the monster truck is too heavy. Even though the truck is heavy, it doesn't get stuck easily and it can climb hills. The only bad part is that it isn't good for tricks, although the truck gets good distance. Hope I helped!
I love three vehicles, motor Monster Truck because it has big tires so it is useful in valleys, Super Diesel 4X4 because it has most powerful engine, large fuel tank, awesome pickup. SnowMobile because it has great gripe on smooth tracks and very helpful at the time inclined valley , powerful engine makes it very graceful.