I'll skip everything and just nominate the Smokeless Image Volt.
Why?
*Volt mah: 220 (roughly little over 2 hours of vape time)
*eRoll mah: 90 (is that right? correct me if I'm wrong) - (roughly an hour and a half of vape time)
*Volt: Carry two batteries with fresh cartridges and you have a good night out, you need nothing more (a fresh Volt cartridge -- if you're using blanks and other vendors' juices -- will last you a day, maybe two days, with topping off here and there, maybe a few drops, easy to do, no special tools required).
*eRoll: Carry a PCC pack (size of a cell phone), with several batteries, you need a needle tip bottle to fill the tank, the tank is finicky, as is the atomizer. You have multiple parts to keep track of and maintain. You will need to refill the tank with the needle bottle constantly throughout the night.
*Volt: You screw a cartridge on and you puff. Done.
*eRoll: you have to fix the atomizer to the tank and then puncture them and fill the plastic tank with a needle tip bottle and... dude, this was so 2011...
Anyway, Volts are easy peasy, deliver just as much satisfaction as an eRoll.
FINAL CALL:
You're drunk in a club. You're in a bathroom. Music is pounding. Which is easier? Screw a cartridge you already primed with awesome juice onto a simple stick battery and puff, or lug out your eGo carrying case with sketchy looking needle tip bottles, a cell-phone sized PCC, multiple batteries rolling everywhere, while other sketchy-looking patrons using the toilets look on... I'm just trying to make your night out easier, bro... ;-)
In My Opinion.