What scale you are using? As the forum members know, I am not a fan of battery power in anything smaller than O scale. In the smaller scales battery fitment can be a real problem in all but the largest of locos. Add in sound and you have a lot of pieces to stuff into an already cramped area. The concessions that must be made are, in my opinion, not worth the benefit of eliminating a few one-time installations of wires and/or reversers. Additionally, battery power raises your cost with each loco added whereas wires do not. Possibly a concern if you have or plan to have many locos. So, my best advice is to first give serious consideration as to why you want battery power and are the trade-offs worth it to you.
With that said, Airwire and RailPro are essentially direct competitors to one another. Neither communicates with the other so it is an either or question. RailPro is far more advanced than Airwire in operational functionality. Most would be sold on this fact alone. However, Airwire works with DCC sound decoders whereas RailPro does not. If you must have a particular DCC sound decoder then Airwire is the right choice for you. Relative to battery power conversion I don't see any difference between the two.