Wow! I haven't seen anybody mention this yet (they probably did but I haven't seen it), but just by changing the e-juice itself I find better results by changing the settings. For example, I have a sample from MBV Maui Sunrise 50/50 and no matter how low I set it (3.3v or 6.0 watts), it vaporizes right away. Higher setting doesn't change the flavor or the clouds much. And I would expect it to be the same until you start getting the burning taste. MBV Maui Sunrise has mostly a pineapple taste plus others fruity flavors that I can't really nail down, but the exhale has a weird taste that I have no idea what it tastes like (it isn't like the inhale and I don't like it very much).
I also have MBV Coffee 50/50 18nic. In a clone tank (2.8 ohms), this behaves much differently. On voltage 3.3v isn't enough, and 4.2v the e-juice burns (4.1v burns a little). Although 3.7v seems to be the best spot for me. In watts, 6.0 it much higher than 3.3v and I only tried this e-juice up to 8 watts. 6.5 to 7.5 watts are very close. This e-juice tends to darken a lot while vaping. It gets so bad it almost looks like black ink in the tank. Today I had enough of it and the flavor was gone and everything. I just flushed the tank with hot water and dried for a bit and refilled. Flavor is better after a few dozen puffs and I have been using the lower voltage or power settings and hoping the e-juice doesn't darken again. Although it only has been a half of a day, I think it is going to end up being solid black again in time even using lower settings. As it looks like it is still getting darker and darker and I am only using 6.5 watts now.