It is not a question as to which one is better, but which one(s) are best for your application. If you have no intentions of lifting in the rear (keepin' it stock), the best would be the 5125s (Sonny @ DSM
will help selecting which 5125s you should use). But if you are planning on lifting the rear in the future, the 5100s in the rear will allow for 3" of lift. Thus, you may want to go with 5100s in case you ever decide to add lift. If you know that you are lifting the rear to a specific measurement (i.e. 2") you can still go with 5125s, but they would be specific to your lift height.
My taco, I have 5100s all the way around, with the front 5100s set at the middle setting and stock suspension in the rear and it sits almost dead level. However, I may put a 1.5" AAL or 2" AAL in the rear and go with OME 881 or Eibach coils in the future. The 5100s in the rear will allow for me to increase the lift (up to 3") without changing shocks if I decide to do so at a later date.
Hope this helps and good luck!