Well, the radio allows your phone to access and relay signal from carrier towers. From what I have learned, people install different radios in an attempt to boost signal reception and data connectivity in their respective area which in turn impacts battery life. No one radio is best for everyone because various contributing factors can impact your and my cellular reception. These factors include proximity to towers, environmental obstacles (mountains, forest areas), the makeup of the building your are in, number of users connecting to those same towers, etc. The less factors in your surroundings then the less time your phone's radio spends searching for a strong signal. The stronger your connection, the better your battery life should be. For most roms your accurate signal strength is displayed in:
Settings/About Phone/Network/Signal Strength
Edit: Also, the radios that users install is software although it affects the hardware radio of the phone.
[VZW] Samsung Galaxy SIII