Itd be nice to be able co compare rides side by side to get an idea. Unfortunately, I think few people have had that opportunity.
reviews say that the 6112 rides really nice, but again will be paying more and it may be harder to find in stock. If you have that extra money to spend, and wont regret over paying, may be the way to go.
The 5100s are the most common and most people are happy with them. They are a 2.0 shock, so in the same class as the fox 2.0, and other 2 inch body shocks.
If nyou wont be off roading, you may want to work at struts/ shocks/ coilovers that are more designed for sport handling/ baja type off roading like the Fox shocks or if you have the money Kings or other shocks that are adjustable
Heres a decent youtube review
Bilstein Shock Showdown - 6112/5160 vs 5100 - YouTube
Toyota 4Runner Coilovers Guide - Fox / King / Icon / Old Man Emu / Bilstein / Eibach - YouTube