Here are the results of (temporary) vehicle speed states:
Fury (boost) ........................................................... 100%
Raptor .................................................................... 83%
Cicada, Scorpion (boost) .......................................... 66%
Fury, Viper, Manta, Scavenger (rolling)....................... 50%
Nemesis (crouch)...................................................... 37%
Scorpion.................................................................. 31%
Hoverboard, Nightshade, Stealthbender...................... 30%
Hellbender............................................................... 27%
Paladin, Scavenger................................................... 23%
Hellfire SPMA........................................................... 22%
Infantry, Leviathan................................................... 20%
Goliath.................................................................... 17%
Nemesis (normal).................................................... 16%
Nightshade (cloaked), Stealthbender (cloaked)........... 13%
Darkwalker............................................................. 12%
Nemesis (Standing).................................................. 07%
Not that this info is SPEED ONLY. Some vehicles are fast, but need to drive around objects/terrain where slower vehicles can climb or fly over it as a shortcut.
Depending on the maps, slower vehicles may be the best choice.
Another thing to note: Weak vehicles can be killed instantly, so you can also use stronger vehicles to make sure you get further in heavier battles, depending on the situation.