Depends upon the flavors that you're using.
Not all
juice flavors enjoy being cooked at high temperatures. Granted I prefer a cooler vape, but I rarely go over 5 volts. My voltage range is between 3.4v and 4.8v.
For fruit flavors, they taste best @ 3.4v - 3.7v, any higher and they tend to taste burnt. I like my coffee flavors between 4.2v - 4.8v. I have a couple of cinnamon flavors that I might run up to 5.6v, but usually prefer them around 4.8v
So, a 2.5 - 3.0 ohm single coil carto works best for me.
Another thing, my experience has taught me that any string-wicked delivery device will have trouble giving nice flavor consistantly. If you think about it, string-wicked devices only have 2-4 strands delivering juice to the heating coil - that's a pretty small surface area.
A cartotank on the other hand has all that polyfill soaked in juicy flavor and totally surrounding the heating coil. That's a lot of surface area. I'll take cartotank over a string-wicked device seven days a week.