This is an interesting question and then the twist was put on it. Solitary Confinement with books or General population with out (books). Okay here's my stab at it. First of all a prison general population without books is like a Roman Coliseum with Rogue lions and gladiators ready to kill other while the guards and the rest are betting who on who would kill whom other first.
The prison population would dwindle because, well people would be dying from unnatural causes. I am not saying books prevent this in a prison atomsphere but it keeps the natives happy at times.
So my answer for this particular scenario is to have books in solitary confinement as opposed to no books and human contact. You do notice I am in third person here. Because I would not wish either situation on myself or anyone else