EV-DO Rev. O and A are both reliable and as a matter of fact, Verizon Wireless in particular (Sprint, I'm assuming has done the same) and have eliminated EV-DO Rev. O and only use the faster one...Rev. A. This isn't necessarily consistent as few rural areas may still have Rev. O (none that I've seen, however).
As long as you're receiving adequate signal from EV-DO, leave it alone. Turning it off may improve battery life...but only slightly. I mean very very little. If you're not receiving EV-DO signal, then turn it off. This will save your battery drastically because your phone is constantly searching for that signal and searching for signal that doesn't exist uses more battery. If you're with Verizon Wireless and receive coverage at all, then more than likely you have EV-DO, too.
You cannot turn off 1XRTT. It won't let you and Verizon requires both of these to use data and 1XRTT is required to place calls. The battery life on 1XRTT is the same or about the same as if you had 1XRTT and EV-DO.
CDMA 3G networks are drastically more reliable and available in significantly more markets than GSM 3G. CDMA providers have had a larger window of opportunity to improve their 3G network and make it better, faster, and available in more locations. Verizon Wireless offers 3G wherever they offer standard voice service...which makes them have the largest and most reliable 3G network. Sprint has 3G throughout most of their network but they are now focusing on 4G.
Hope this helped.
