What's the go to extinguisher type/brand?
Short answer, as always, "It depends." There was a very long extinguisher thread on this board a few years ago with good contributions from an actual well trained firefighter. Search should turn it up. I went with Halon because of all the electronics on modern trucks (mine is an '05 and the newer ones are even more electronically dense). Halon is pretty much banned for new production, so expensive to recharge, but there are substitutes available that are not as effective. If you drive an old rig like a Jeep or a Bronco, Halon or substitute is not necessary and not even optimal. If you are worried about flammable liquid fires (oil and gas), then Purple-K is probably the way to go. If you want to keep it simple, then go with USCG-approved dry chemical units. Some of the extinguisher manufacturers have comparison charts on their websites with a lot of good info.