Hi...
...probably the other thing that might factor in is availability....so many things are out of stock that I dream of a link on some sites that simply list things that are "in stock"....
...the other thing is that the (awesome) genesis style atty's kinda need to be kept upright... always... so if you plan on putting stuff in your pocket, or for allowing it to be horizontal... you mill need to consider cartomizers (with, or without a tank), etc...
so..with regard to what I think is available now, retail (aside from the classifieds, etc)
...I think both the P+ (
Super T ~ PrecisePlus Units), and the very pretty Themis (
Mod themis - Titanide) are very cool...both don't seem to designed to rest upright... the Provari is rock solid, (and it also serves the dual purpose of checking an atomizers' resistance when working with a rebuildable). I think I would recommend the Provari to start. It stands up well, is why I started mentioning it.
...I also see some lengths of the Gus are still available today... pretty, and seemingly flat on the bottom as well:
Devices
...rba's are pretty sweet, if keeping your mod upright is cool w/you (I'll be happy to hear any corrections, or thoughts on this)..
...so I think the AC9 looks great.. available probably for a few more minutes at:
AC9 Kit – Vapinaze
...and this cobra looks very nice, available at the moment:
Cobra Atomizer
...anyway... just a few thoughts.. good luck, & cheers, ~M