If I had to pick betwen the jeep and the toyota I would pick the jeep just for the vast aftermarket
BUT if I was going to build a offroad toy I would buy a later 70's early 80's K5 blazer
have a ton of aftermarket, the majority of the parts are easy to come by and are cheap
They are VERy popular Platforms for offroading toys and for good reason, Granted they won't win any gasmileage awards but it would more then make up for that with Instant Power you can easily mod the 350 to geet 5-600 + horse power you could go more depending on how exreme you wanted to go
OR if you wanted something Really Extreme check this Vid out