What is the easiest physics engine to use ?
(esp.for ragdolls)
and what has the least bugs?
Well normally the most important is not what is the easiest. The question is... which have the better manuals? support? samples?
I am using ODE because it is easy to make a vehicle simulation. People says that for individual objects Tokamak is better.
I have tested both, and the documentation of ODE is awesome.
Now there are some new libs, like TrueAxis, very promising.
I suggest you to try both, ode and tokamak, and decide for yourself... Both are not very difficult to use. The problem is, however, the tunning of the simulation.