My favorite vehicle in Halo 5 would have to be the ultra banshee simply because of the triple explosives in the fule rod cannon, the banshee flight itself is something i have practice and expertise. - wasp are also pretty cool, not a fan of early combat in warzone though.
To be honest, even with much heavier vehicles to choose from among all the variations of Wraiths, Scorpions, etc. the one that I’ve probably used the most in WZ and FF is the Ghost. Fast and agile enough to zip around in places where those heavier armored vehicles can’t. It’s not my first choice when Mythic bosses spawn obviously, but it’s probably the one I’ve overall used the most.