Update on the AT&T GoPhone SIM. I had issues at first, but after talking to AT&T Tech Support, they walked me through setting up an APN. Now it works well. More on that here:
http://forums.androidcentral.com/lg-g4/535360-t-gophone-not-working-my-global-g4.html#post4463896
I haven't made a ton of calls yet. Only 1 to myself. It sounded good. I'll be using this to make most of my calls and let you know what others say.
So, signal strength:
iPhone 6 Plus:
View attachment 179314
LG G4 (Note: this was before the APN setup, but even after, the signal didn't change):
View attachment 179315
So, with 4 dBm, there wasn't a lot of difference between the 2 devices.
Speed Test:
iPhone 6 Plus:
View attachment 179317
LG G4:
View attachment 179318
It's hard to blame the device for these results. AT&T has never been great at my house. That's why I'm on Verizon. I did have faster upload speeds, but then my download speeds went down.
For an AT&T vs Verizon contrast:
Here's my
Verizon speeds taken a few months ago. Early morning, but still my speeds on Verizon at home average around 30Mbps all day.
[url]http://i870.photobucket.com/albums/ab262/scottysize/Droid/Screenshot_2014-06-24-05-26-42_zpsa0dxw6zs.png[/URL]