I have a GS4 and my wife has HTC One (LTE) and we just bought 4 Galaxy Lights about a month and a half ago and haven't had any issues with them. The first month all the kids blew threw their 500mb of High Speed Data in 2 weeks. While we only have 2G where we live and just use Wi-Fi we are only about 2-3 miles from LTE so when we go to town they tear the data on LTE. The only issues we have had were that after the Wi-Fi calling outage last week one one of the SGL's had to keep having the 911 address updated everyday to keep the Wi-Fi calling on but after having T-Mobile update it from their end it seems to have stuck.
I have seen a lot of threads on this forum with the IPhone and reception issues, it does make you wonder if something in the baseband needs to be tweaked especially since the T-Mobile 1700 Mhz band is a new frequency for the IPhone. I would also be nice if Apple would support incorporating Wi-Fi calling in the OS/Baseband. Now that Sprint is also adding Wi-Fi calling (albeit with restrictions) maybe Apple will finally support changing the OS to support it.