dspoon,
The Quick Connect fittings duplicate the factory connections already found on the tank module, so you'd want to choose those if you either A) intend to use the stock fuel lines and connectors, or B) you plan to replace the file lines, but you still want to use the same type of connections to the tank the factory used. The Quick Connect fittings make disconnecting the fuel lines from the tank quick and easy. The downside to these fittings is they can potentially leak if subjected to physical abuse or pulling stresses. This probably isn't a concern for 99% of trucks.
The Push-Lock fittings have a special hose barb to a male NPT thread. This can be considered more of a direct permanent connection of the fuel hose to the Draw Straw and it can't be quickly removed. You pretty much have to cut the hose off the barb to get it off. It won't work with the factory connectors on the factory fuel line.
The factory fuel lines are:
Suction - 3/8" Quick-Connect
Return - 5/16" Quick-Connect
Best regards,
John L.