From my understanding:
EPass works the same as the SunPass just from a different agency
EPass Extra is essentially a SunPass and EZ Pass combined.
SunPass is same as a EPass but issued by the state.
E-Z Pass can be used on CFX roads in Florida plus all EZ Pass states.
If you want the benefit of the EZ Pass plus the ability to use it where the SunPass is accepted, the EPass Extra is the way to go.
There is talk that EZ-Pass is the system many other states are considering when incorporating other systems into their own. I can see the day where EZ_Pass will be accepted in most if not all states. CA and TX have been studying the ability to accept E_Z Pass within their systems.