Only difference I see is the standard ego battery - $21 vs $26 .. the usb's and megas seem to be on par.
I guess it depends on the shipping and how quick you want it. With HV you'll get it sooner as NicFit is in BC.
I've got ones from both and they work fine. Only thing I found is with the T-Rex battery I bought from VaporsKitchen, the eGo-
tank atties don't seem to work. They work fine on regular ego batts but for some reason this trex wont fire those atties.
edit.. wow guess i don't read well these days.. I see the $6 difference in 510
batteries. I can't imagine the quality is any different on those or the egos though.