I'd take one of these:
Ford Raptor F-150. I would possibly swap in a bigger diesel engine, probably one of the big TurboDiesels from Ford's lineup, depending on the severity of the situation. Either way, its 4WD, sturdy, has plenty of ground clearance, and it will do 120 mph.
These are the modifications I'd make:
Simplified Intake and Exhaust (More HP)
Put a massive cow-catcher type rack on the front (And weld nails to it for crowd control)
Gun racks- Enough to hold two 12-Gauges, five Pistols, a 7mm and two AK-47s
I'd cage-in the windows
A rack in the bed for some type of motorbike (Quick getaway in case of engine failure)
I'd also add basic armor around the engine block and cab (But not in a way that would cause the engine to overheat)
In my opinion, its the most reliable, most accessible zombie-slaying machine out there. It would at least last until Element 115 wears off. (My Nazi-Zombie slaying friends would know.
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Anybody else agree?