I would say the best is the 4runner you own, because otherwise (gasp!) you'd be in a Jeep!
Seriously though, I think any IFS truck requires a locker to do serious trails. Not enough suspension travel to reliably keep all wheels on the ground when it gets uneven. So, if you want to go stock, you have to stick with the generations that could be bought with a locker. My next criteria is ground clearance and approach/departure/breakover angles. Hard to beat the 3rd and earlier generations for that, just because of their smaller size.
Once you start adding your own stuff, you can build about anything you want. My lowly 2nd gen, with mods (see signature), holds its own on some pretty gnarly trails.