Im personally a really big fan of the whole Zenesis 2 lineup.
The whole lineup is modular. Everything fits on everything.
You've got
Body Tubes-18350, 18490, 18650. Stainless, Gun Metal Nanocoat, Brass, Sapphire NanoCoat(soon to be released)
Small Tank Atomizer
Large Tank Atomizer
Carto Tank, will hold 35mm and 45mm cartos
510 Connector
So, you can have any mod you like. Want an 18650 Genny Hybrid? No prob. Want an 18650 Carto hybrid, so you can run with a kick and an 18490? No prob. How about an 18350 genny hybrid, but you want the big tank atty? No prob. How about an 18350 mech? See where Im going?
Everything fits on everything. AND, everything is pretty much always available, with the exception of the carto tanks/carto hybrids, those have been in high demand and sell out quickly. But otherwise, Zen and ElectronicStix have been doing a great job keeping everything in stock.
I purchased a gun metal Altus, and a DX350. Which is an 18650 big tank atty genny hybrid, and an 18350 mech. But, I can turn those into whatever combo I want.
I am totally loving my Altus. Its really a piece of art, and definitely my nicest device. I tend to only put my absolute favorite juices in it. And the 18350 mech is just as nice, and its seeing just as much use, mainly with my RDAs.
I definitely plan on purchasing some more Zenesis 2 pieces.