Battery Life? Very important.
Throat Hit? Subjective, high nic is too harsh for me, SB at 6v nice mild hit at low nic strengths. Would love to replicate that kinda full 'mouth hit' cigs gave me.
Ease of Refilling Cartridges? Sure.
Longer Lasting Cartridges? A consistant long lasting cart that is easy to refill would be nice.
(an aside on carts... stopped using them completely. Pain to clean, refill, top up. I find dripping is like how I used my lighter with analogues. Pull out my little carry juice bottle, few drips, and bam my e-cig is 'lit' and you know when your e-cig is 'out' same as if you dragged down to the filter on a regular)
More Vapor? SB at 6v is more than enough.
Less Vapor? Ummm, no.
Better Flavor? Not an issue, too subjective.
Size? Smaller is better, portability is my ONLY issue with an SB.
Best thing about 6v I find that it comes closest to replicating an analogue: instant gratification. No primer puffs (though I do enjoy 'puffing' on my regular 510 like a pipe), no warming up the atty, just hit it and get a consistent experience everytime - like an analogue.