I say AdapteveR -- tough as NAILS! (Maybe PM Skyycamel, for some guy talk about it!) I've ended up with two, since this is the kind of mod you marry lol. Built with all-mechanical parts, and has common user-replaceable parts that can be found at any electronics store, a big plus.
Can get additional connector tip ('insert') styles if desired, not locked into just one. Does have an end button, which I like just fine, and of course helps facilitate the great features above. Not
known for going off in pockets, however if you want to cover the end for good measure, a "lighter leash" fits great. It's a rubber cap thingy with clip-on cord (that you can remove if you want) normally used for keeping a bic handy. Got mine at amazon, but can be found at many convenience stores and gas stations. Can see a few style examples at lighterleash.com.
Can get a sleeve for 6V vaping with the AdapteveR
if you want, including one that takes protected batts. That's what I use and love. (As a 'treat' tho -- I discipline myself to use 3.7V most of the time.

) Cartos at 6V don't taste harsh or burned, the way some feel standard atties do, myself included.
Search by AdapteveR, you'll find lots. (There's always adaptever.com too, but there's more to be found on forums.) Been around a long time as these things go, with a great rep for quality and toughness. Just not as much buzz since the guy who builds them (posting name "WhateveR," real name Thad) doesn't have his own forum here. (Tidbit, he posted on another forum that he's in process of designing a new mod now... Hmmm, I'll be watching, tho I think I gots me enough mods already and I do feel plenty 'fulfilled' lol!)
FYI, great deals can be found on most mods in the classifieds here from established members, some who 'chronically' buy sell and trade so they get to try everything. Well, good luck!
P.S.: There are adapters to make all mods/batt connector styles work with cartos. A 901 tip may not
necessarily work with cartos out-of-box; altho they may screw together fine, the holes/slotting won't necessarily be correct. Ask the modder, or some adapt 901 tips themselves if not carto-ready. Myself, I didn't like how cartos vaped on a 901 tip via adapter, tho maybe it was the adapter itself. Choices seemed to be either all air or no flow at all, but I think that's what Skyycamel uses so dunno. I like 510 tip and carto adapter. At first seemed airy, but once I realized the adapter's center section moves I got the hang of it and it's great now.