The new V2 EX blanks have a screw top now, but I also like the e-Smart clearos better. The V2 blanks can vape almost uncomfortably warm (for me) on a fresh battery. The e-Smarts are a bit wider than a standard V2/808 slim battery, but they hold a little more liquid, are less expensive, and seem to last longer overall. I like the wider e-Smart batteries and use both e-Smart and V2 clearos on them.
I actually prefer the smaller 808 batteries/clearos to the more popular 510/eGo setups when not using a full-size mod. They're just so portable! Stick two or three 808 batts with loaded clearos in your pocket or bag and you're good to go for several hours with a variety of flavors so you don't get bored. I really like the tighter draw on the tiny top coil clearos, the better balance with the battery when filled (as opposed to top heavy mini tanks), and they're great for giving new juices (and interesting flavor mixes) a decent test run without wasting a bigger tank and coil.
I even wound up buying a couple of 510-808 adapters for my eGos and Spinners so I also could use my 808 clearos on them instead of my mini PT2s and EVODs. They do make 510 threaded e-Smarts, but I already had a nice supply of the 808 version after my oldest 808 batteries gave up the ghost, so the adapters were more practical.