(Something unusual happened one time I drove from Ganton towards the Vigilante test site. I started Vigilante already in Ganton (I just started it without caring about the mission), and without ever getting near the suspects I got to level 4 as I drove the freeway north towards Montgomery. I didn't look on the map exactly where the suspects were, but they were south of me. I didn't do anything beside beelining for the test site at Blueberry/Panopticon. My Vigilante test Enforcer gained 900 HP already before the test began, but I reset the health to 1000 with a cheat code.)
My Enforcer vs Barracks test results:
Enforcer: I don't think I cleared level 6 but I came close several times. I often cleared level 5, and also often failed before level 5. Surprisingly often I failed on level 1 and 2, it is very difficult to deal with suspects on motorbikes. This is a problem with a slow Enforcer, but an even bigger problem with the even slower Barracks.
Barracks: I cleared level 6 several times but never cleared level 7. Generally I got one level higher than with the Enforcer. Barracks actually have a higher top speed than Enforcer, but the acceleration is so slow that you almost never get up to high speed. The grip is superior, but you can only make use of it the few times you need to go off-road, or when it rains. Because the truck is so slow you only can crash suspects when you meet them. I find that when I drive after my suspect it is hard to catch up with them and I have to leave it to my passenger to destroy their car.
I thought the same but have changed my mind! Having two backup homies in the back of an Enforcer is not an advantage, it is a disadvantage. When I use an Enforcer I no longer take with me more than one homie. Why? Because the brainless homies are too damn slow, once they get out of the vehicle it takes them too damn long time to get in again. They are less smart than a chicken and CJ can't order them to stay in the vehicle when he goes out. And they don't even act smart when they are of foot! They are only useful when they are in the vehicle and return fire. It is more efficient to drive back to the other side of the world and recruit a new homie if he dies.
One bonus the Enforcer possesses that the Barracks & Ranger doesn't is occupancy space. If you embark on the Vigilante mission with a recruit who happens to get killed, you're on your own; if you use an Enforcer, you can have two backup recruits sitting in the back at your disposal, though the problem is that they don't all shoot at once, but only the front passenger does.
I can testify that a Hunter that has completed 500 levels of vigilante is very difficult to destroy. AFAIR it took several minutes of sustained minigun fire and over 100 SAM hits to destroy it.
500 x 300 = 150,000 added HP!
I don't know how much health a rocket takes, and if SAMs are more or less powerful than RPGs. But 100 hits is a lot.