I had a 1st gen for a few years and while I liked the truck, the 22R-E 4 cylinder was just too gutless, I didn't enjoy driving it. Had it been a turbo or a V6, I would have kept it longer. It was pretty rough and not very quiet.
I sold it and bought a 2nd gen V6-speed. People complain about the power of the 3.0 but with the 5 speed it's not bad at all. It didn't sound like it was struggling like the 4 cylinder, the engine was actually pretty quiet and refined. I put a lot of miles on that truck and liked pretty much everything about it. Yes, the power to fuel economy isn't that great, but otherwise a great truck.
When I found a 5-speed 3rd gen 4Runner with the e-locker I jumped on it without thinking. It has everything my 2nd gen had plus more power and better fuel economy. The steering and front suspension on the 3rd gen is better than the 2nd gen, so basically the 3rd gen fixed the short-comings of the 2nd gen. I later supercharged it and now it has more power than the 4th and 5th gens.
I like the 4th gens too, but with no manual transmission, no elocker (or at least rare since they only made it one year on one rare model), very low to the ground compared to the 3rd gen, I don't really see it as an upgrade to what I have. They are quite a bit bigger (if that appeals to you) and the 4.0 makes more power than a non-supercharged 3rd gen. Toyota quality is still there, the interior is nicer than a 3rd gen and they are more luxurious. You basically trade the 3rd gen's out-of-box trail worthiness for luxury. You can get that trail worthiness back with a lift, larger tires and an ARB locker, but you mentioned your desire to not do that.
The 5th gens aren't appealing to me at all. They're too big, too ugly, seem to have some quality issues and generally doesn't have a 4Runner feel to me. It's just not appealing to me, but I think they're a decent rig. I would buy a 100-series Land Cruiser or a Lexus GX470 before I'd buy a 5th gen.
Hope that helps. In general, I like 3rd and 4th gens best.