Dill, if you're going to order a new, true 3.7v Riva, I recommend the Boge cartos, either 2.0Ω or 3.0Ω. The 2.0Ω ones are perfect for the 3.2v standard eGos and Rivas, but with the 3.7v device, you can use the 3.0Ω also. It depends on your preference; if you like cooler vape, go with the higher resistance, if hotter, choose the lower one. They will both work fine. You'll just have to be a bit more careful with the lower resistance Boges on higher voltages--they are more likely to burn.
My favorite setup is a new eGo-t atty and tank cartridges and/or the Boge 2.0Ω cartomizers. I do not care for the CE2 fillerless cartos; I tried several different revisions and none worked out of the box. They need to be seriously modded to work well--not for the faint of heart and not for the new vapers. There is a VERY long thread about the Revision 4 CE2 cartos in the cartomizer general forum, if you care to read it. I believe that they will eventually get better, but the design has to perfected, IMO. Besides, they are a PITA to fill, clean, torch etc... Don't bother. At least, not yet.