IMO it's all about the sweet spot.... perhaps AKA wattage....
I've had great
vaping at 3.2 volts, and I've had great
vaping at 6.6 (and terrible at 3.2 and 6.6).... a good vape depends on several factors- the voltage, quality of the atty, resistance of the atty, and the nicquid blend... I've found atty's i really like for use on a single lithium cell (4.2 volts to 3 volts), and i've found a lot i hated on that voltage range... and i can say the same for higher voltages....
btw... just to clarify for noobs... take an eGo for example... when fully charged it sits at 4.2 volts dc..... then as you use it, the voltage slowly drops.... i haven't measured one when it was nearly exhausted, but I'd speculate around 3.2 volts... so just to clarify, an eGo will indeed put out 3.7 volts at some point, just not for very long, the more you use it, the lower the voltage will be... then you recharge and start again at 4.2
which brings up why having regulated voltage is such a big deal... if you find you enjoy the vape of your eGo when its fresh off the charger, then it's not so good when you've used it for half a day, buying a unit with regulated voltage could make your vaping a better experience, as it will put out pretty much the exact voltage that you select on it... you don't have a good vape at the beginning, an ok vape in the middle and a poor vape when the battery is nearly empty...