Although perhaps not quite "objective," I think most people would agree that the three-button implementation of the user interface used on the Vtube (especially the Young-June versions) is more ergonomic and user-friendly than the single-button menu system of the ProVari. The ability to check atty/carto resistance, voltage setting, and battery-remaining graphic all together with a single click of the power button on the Young-June Vtube is much easier and more elegant than the multiple-click-and-wait routines used by the ProVari.
How important that feature is varies from person to person. Some don't care at all and love the ProVari for its heft, what-you-set-is-what-you-get voltage, build quality, and warranty service. For other people, the user interface is an important consideration and may affect their buying decision. Different strokes for different folks.
That was one of the reasons I didn't order a ProVari until this week. The $40 off chrome blem ProVari clearance sale finally got me to pull the trigger. Soon I'll have a ProVari to go with my BuzzPro and iPro; Vmax v2; Ovale V8; Vector VV, Varitube X, and Chrome v2.0 Young June Vtubes; four eGo Twists; and 13 other plastic or wood VV box mods.
Oh boy, I'll be qualified at last to join in the melee on all the ProVari versus Everything Else thread wars! LOL.