Apologies to the O.P. but it's very difficult to work out what people are talking about when they refer to eGo-C and eGo-T and eGo "any letters".
The eGo bit is the battery.
It's what you attach to it that matters.
My opinion (as direct and eGo-maniacal as ever) is that any joyetech system that utilizes the "revolutionary tank system" that uses an atomizer and cartridge is really only destined for the bin after a few uses.
As far as I can see there's only one device called a joyetech eGo-C. There are a load of knock offs, of course.