I will stay with ATT as Verizon is too expensive and TMO in my area has sh**ty reception. ATT has been perfect for me in that area.
Also, I have been a heavy flasher for almost 4 years. The phones now are powerful enough that flashing roms is not that important to me as it once was. If I can get root with Xposed/Gravity Box/3Minit I am good. Plus there are fairly good backup apps now that Nandroiding isn't that critical.
I don't see much more coming my way, after this year, in improvements I am interested in. Something like a Note4 or S5 would be as far as I care to go.
All IMHO of course
ATT Samsung Galaxy S4/Rooted/TWRP 18.104.22.168/KT, Faux, or Audism Kernels/3 Minit, Wanam Xposed, or Gravity Box/Long Time MultiRom Flasher