While I don't have two tmo LTE phones, I did switch from straight talk and my tmo LTE is horribly inconsistent while the ATT LTE signal on the same phone is solid wherever I had reception. It also has a weird issue with speed test in particular where it keeps routing me to a server in Denver or Albuquerque even though the location services work fine.
Tmo hspa isn't great in my area but still more consistent by far. I may just switch back to straight talk even with the cap as I have zero issues on ATTs LTE network and don't stream anything other than music. The phone is by far my favorite, even compared to my friend's N4 (the camera and screen spoil you, and I can't see feeling the need to upgrade for a few years now that I have a camera I'm satisfied with)
edit: t-mo LTE is -103 inside or out, ATT LTE is -88 with excellent and consistent speed (ping is a bit higher at 240 as prepaid often is, but that's fine for everything I do). And it's certainly not an issue of grip, as I actually get better ATT LTE while holding it than setting the phone down