I found that doing both, the rebuilds and cartos, are great for me. Like brook, I screwed up and ordered 2 19mm XL IBT, when I already had 1. I need a 22 for provari and mech mod. I have found, however, there are certain juices (fruit type mostly) with cartos that don't give me the aha moment. For those I go with a pt2 or nautilus. The russian that I picked in a coop, will one day show up. I'll see how that goes.