Here my personal experience:
Vivi nova....soooo easy to use. flavor does die out over time (about 3days-week) for me. changing flavor sometimes helps. next step, take it apart, rinse, refill. last step just replace the head. I tend to replace the head after about a week. Heating over time tends to thicken the liquid and it doesn't wick quite as well as fresh liquid. That is a problem with all except the dual coil tank and dripping. Its just the nature of the liquid.
Kanger....sooo easy to use. after a couple of days I end up getting the burnt wick taste....more than likely it doesn't like my stronger flavors...seems to do well with my lighter fruit flavors.
Dual Coil Tank....A bit more fuss to fill, but the flavor seems to last longer and more consistent vape...usually end up changing the cartomizer every couple weeks (draw gets tight, filler clogs).
The eGo 2.4 ml CC long wick is another clearomizer I like...the only problem I have had it the past is the tip can break away causing it to leak (super glue fixed that). I like it as much as my vivi nova.
http://www.theveteranvaper.com/ego-2-4ml-cc-long-wick-changeable-coil-clearomizer/
Dripping....This for me has been my sweet spot for a very long time. better flavor all the way around. But it is a bit more work and a bit of a learning curve.
the 4 I always have on hand are the vivi nova, dual coil tank, eGo CC and dripping. I have a tendency to rotate through them....each one is just a bit different, and each one usually has a different flavor. (except dripping....that is alot different). I still mess with the kanger, because I like variety I guess.....
sorry, Long answer.