From my expierence juices that are more black than anything else gunk up my atomizers very quickly, regardless of the Pg/Vg content of the mix. Although, the higher the VG it seems to kill my atomizer even faster than higher Pg mixes. I know some people beg to differ and claim that dark
juice is not the culprit but instead it is the VG content, sweetener and even some oil based flavorings that vendors like to add to their liquids.
This is why I usually like to stick with around 20%VG, juices that are very light almost clear in color and do not contain sweetener. With that in mind, I have atomizers last me in upwards of 6 months without ever cleaning them, soaking them or dry burning them.