Not trying to start any wars here, but would like to educate myself.
The only experience I have is with the 4081, but when I look to see who's using what, the 4081 and the 510 seem to be the 2 front-runners. Both seem to have roughly the same amount of after-market parts (passthroughs, etc.) available for them.
Which got me to wondering - The only difference I think I've detected between the 2 so far (and correct me if I'm wrong) is that the 4081's atomizer is activated when you drag on the e-cigarette, and the 510's is manually activated by pushing a button.
I read that the 501 is supposedly better for dripping because of this push button. So I was hoping that those who use one or both of these popular models can tell me (us) why you chose that model, and the strengths and weaknesses of each, as compared to the other (or similar) models.