said by en103:Sprints newer phones are both - question is - how many Sprint users are on LTE in your area, and what is the cell density like ? I'm sure that VZW has a high percentage of its data users on LTE.
That leads to a good point though. Given that Sprint LTE is on 1900 it means there is more density of sites so you are likely to be closer to a tower and have fewer users per tower, especially since Sprint has half users of ATT/VZW. ATT/VZW are doing LTE on 700Mhz so a tower may be further away, which impacts latency (and supposedly 700Mhz is susceptible to interference more than 1900). Downside to 1900 is distance so needs more sites but that means since sites are closer together, you are likely closer to a site so you're likely to get lower latency. So there may be more variance in latency on 700 LTE than 1900 LTE - can't speak for HSPA+ on 1900, maybe protocol slightly less efficient.