I would choose a Bronco (solid front axle smaller one) any day, any time, without any hesitation, over a grand or Cherokee to build big for off-road. I wouldn't even need a second to think about it. I know this is a jeep board but, I wouldn't want to build a unibody if I planned on keeping it for an extended period of time or going big.
X2, I just wouldn't build a unibody big period. Unibody designs are very stiff but they aren't strong. Remove any component like the doors for more fun wheeling and the strength is greatly dimenished. As in if you wheel it hard enough, you may not get the doors back on or back to where they will close right again.