Here are the different model numbers and specs below, found here under "Cellular and Wireless". To avoid confusion, I'm only listing the 5.5" models, although the 4.7" are analogous:
As you can see, Model A1524 is clearly the model to get as it has the most available bands. The problem is, I can't figure out which carrier this is tied to. Is this the Verizon one? The Sprint? The "unlocked" version (if that even exists at this point)? If anyone knows how to tell which models tie to which carriers, please let us know.
Model A1522 (GSM) (Probably the AT&T / T-Mobile version)
Model A1522 (CDMA) (Probably the Sprint / Verizon version)
Model A1524 (???)
UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz)
GSM/EDGE (850, 900, 1800, 1900 MHz)
LTE (Bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 18, 19, 20, 25, 26, 28, 29)
GSM/EDGE (850, 900, 1800, 1900 MHz)
LTE (Bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 18, 19, 20, 25, 26, 28, 29)
Model A1522 (CDMA) (Probably the Sprint / Verizon version)
CDMA EV-DO Rev. A and Rev. B (800, 1700/2100, 1900, 2100 MHz)
UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz)
GSM/EDGE (850, 900, 1800, 1900 MHz)
LTE (Bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 18, 19, 20, 25, 26, 28, 29)
UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz)
GSM/EDGE (850, 900, 1800, 1900 MHz)
LTE (Bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 18, 19, 20, 25, 26, 28, 29)
Model A1524 (???)
CDMA EV-DO Rev. A and Rev. B (800, 1700/2100, 1900, 2100 MHz)
UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz)
TD-SCDMA 1900 (F), 2000 (A)
GSM/EDGE (850, 900, 1800, 1900 MHz)
FDD-LTE (Bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 18, 19, 20, 25, 26, 28, 29)
TD-LTE (Bands 38, 39, 40, 41)
UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz)
TD-SCDMA 1900 (F), 2000 (A)
GSM/EDGE (850, 900, 1800, 1900 MHz)
FDD-LTE (Bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 18, 19, 20, 25, 26, 28, 29)
TD-LTE (Bands 38, 39, 40, 41)
As you can see, Model A1524 is clearly the model to get as it has the most available bands. The problem is, I can't figure out which carrier this is tied to. Is this the Verizon one? The Sprint? The "unlocked" version (if that even exists at this point)? If anyone knows how to tell which models tie to which carriers, please let us know.