The Classes:
Moto: The Mohawk 66 is the best between the motos. It has quite good handling and good acceleration.
ATV: Sometimes you will use the second ATV (especcially for the longest tracks like Mud Blow or Anguta Glacier) because he has better speed and acceleration. Handling is very inconfident.
Snowmachine: The lunatic one seems to be the best between the 3 vehicouls: it's not too slow and not too inconfident in handling.
Buggy: Very useful: if you have the possibility pick the buggy class: Acceleration and good handling are the best quality for this class (and more thoughness than Moto).
Rally Car: Top speed but bad handling: if you pick a rally car you have to be aware of the suspension: Usually, pick the first rally car is better than the others (due the instability of suspensions).
Snowpugglers: The only reason to pick it is that they are thoughness enough to resist to Big Risg. Lunatic car is the best one.
Snowcat: With the buggy is the best class to use: The Patriod Compadre let you dominate every event !
Big Rig: They are really thoughness but also really slow: be careful when you pick it overall in the high levels of the festivals.
The Choise:
Short tracks (Gold Rush, Log Jam, Wolfpack Mountain and Widow Maker) --> Motos and Buggy (sometimes also Snowcats)
For the following tracks: Nothern Face, Vertigo and Eagle Falls --> Buggy, Snowcats
Fast tracks (Mud Blow, Anguta Glacier and Snowgod Canyon) --> Rally Car, Motos, Snowcats (and sometimes Snowpluggers)
Hard Tracks (Ascension and The Chasm) --> Snowcat and Rally Car