If you're going to get a Twist, DEFINITELY get another kit for a backup. Dont even waste your time and money with either the eGo-C or the eGo-T. They have far too many problems with those tank systems. Most people ditch them pretty soon and switch to clearomizers or cartomizers anyway.
I'd suggest getting a kGo kit for a backup. You can use the same cartos, etc. as the Twist. You get 3.7V instead of the wimpy 3.4V of the eGo. You don't have to buy special tanks or atomziers or cones or any of that crap. You won't be frustrated with leaky tanks.
The eGo-C's and Ts are glorified cartridge/atomizer systems. They call the "tanks" but they are not. They're cartridges. The only difference between the T and the C is that the T is a one-piece atomizer and cone assembly.
If you get a kGo or Riva or something without all that junk hanging off the end of it, you can just get Vision Clearomizers, or cartomizers or a cartomizer tank, which is a real tank and not a cartridge. All of it will be compatible with the Twist.
If you want the lower power of the eGo, at least just get the eGo without paying for a bad "tank system". Use the money you save to buy a couple of eGo Vision Clearomizers. If you want something with a little power, get a kGo instead. It's 100% compatible with everything that fits on an eGo or a Twist and it costs less.