I do know all about the DUKWs. Damned fine vehicles, but yes, spare parts are going to be a biotch.

And for lots of the parts, you're going to need a welder and some sort of machining ability.

However, we'd also have to define what this apocalypse is going to look like. Is it the post nuclear war? The ice caps melting? The world falling into general anarchy? Some pandemic killing 90% of the population?

Wow - this list could get very entertaining...

Honestly - things like GM and Ford trucks (mostly the Blazers, Surburbans, and the like) are probably best. The Jeep is good to a point - but not really all that big. The others could probably do a better job in terms of security while doing a decent job of getting around, are reliable as hell, and spare parts really aren't an issues (for serious - how many Chevy small blocks are out there? If that doesn't make it easy to get parts...).