The Gingervaper Boxer Classic BF Mod has a custom made 510 as well as Rhodium plated Beryllium Copper contacts. There is little to no need to clean them and they should end up having better conductivity than most of the rest on the market right now. It also comes not only as a single 18650 but also in a 2X700 version (compatible with 20700 as well as 21700 batteries), which is a tiny bit larger.
21700 - Samsung INR21700-30T should become available within the next few months and this seems to be just a dream come true for me. I am not willing to spend hundreds of bucks on a mech mod, that still uses 18650 batteries.