IMO a VV device is more versatile that a single voltage device. On my 5V box-mod I only use cartos and attys in the 2.8-3.2 ohm range. Any lower than that it tastes burnt; any higher, the vape is too cool for my taste. The exception is 1.5 ohm DCC: they rock at 5V, but then they are two 3ohm coils. On my VV I can use any carto or atty from about 1.5 ohm up to 4.2 ohm.
One thing to keep in mind about the LavaTube: it is limited to 2.5A so if you use a 1.5ohm DCC you will not be able to push it past 4Volts or so. If you decide to go VV, look into box mods or the LavaTube, or if you have the cash to spend go with the Provari or Darwin. There also a number of other devices that are very good: Buzz Pro, Saber-Touch, etc.
Good luck...