I like the ones that are easy to fill and stay consistent for a long time. They are hard to find.
Some brands change from one order to the next and it's a bit of a crap shoot each time. Once you eventually find a model that is easy to fill the next time around it won't soak up hardly any juice at all. The change the batting material it seems.
Then, of course, you have the coil issues. I used Boge's for a long time and was pretty happy with them. Then I got a batch with bad coils, two boxes worth, all bad. That was a good chunk of money down the drain. (The supplier didn't answer my emails about the subject)
So finding a good model can be hard to begin with, and finding one that is consistent is even harder.