Off the cuff, if you are wanting to stay in the cig-a-like arena (and it seems you do), the Volcano Magma comes to mind ...but at best I'd say they are about equal rather than one is 'better' than the other.
The G6 and the Magma are both 510 threaded and you can pretty much get 510-threaded cartomizers anywhere - Boge, Smok, etc. The thing is, they are all pretty much made by the same factory in china so the chances are pretty high that the G6 and Magma carts are (likely) Boge carts to begin with.
It may just be that you are ready to step up to an eGo device. This is the natural progression and evolution for most people. eGos are slightly larger (about the size of a medium cigar), but they open up a world of potential in how long you can stay away from a power outlet or a juice refill bottle. The
Twist/Spinner combo found at MyVaporStore with a couple of Evods is quite possibly the best deal in town for someone looking to trade up. You can still continue to use your cartomizers on these (if you have any left over or choose to do so), but most accept using the Evods pretty easily.