Best off contract version (ATT, VZW, TMo, Sprint) to buy and how to pre-order?

[blulegend]

If you could get any version (ATT, VZW, TMo, Sprint) off contract, which to get? And how to pre-order it?

Asking because of the base bands on the different versions are different. Or will off-contract automatically have all base bands?

Cutting and pasting from Apple's website the bands:
Model A1549 (GSM)*
Model A1522 (GSM)*
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 A1549 (CDMA)*
Model A1522 (CDMA)*
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)


Model A1586*
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)


All models
802.11a/b/g/n/ac Wi‑Fi
Bluetooth 4.0 wireless technology
NFC