Well, I can say that the vape on the Yihi-powered IPV D2 is "cleaner" and more accurate than the eVic VT (which has been proven in testing to be "underpowered" at a given temp compared to other boards).
But the eVic Mini has a much much nicer screen, a (slightly) better interface, a (hopefully) better/more durable finish on the housing, a traditional micro USB charge port, it's more attractive looking, and Joyetech QC is among the best in the Chinese mod business (Pioneer4You, not so much).
Even so, for me, the D2 is still the best choice, mostly due to the Yihi board and the extra 15 watts in Power mode.
Also, the sleeve on the D2 is dead simple to slide on and off. I can have it off in a second, pop the battery door, pop in a new battery, replace the door, click five times to power up, and have the sleeve back on the device before it's done booting up, without removing my atomizer.
And even with the sleeve, you can change batteries a damn sight faster than dicking around with that screw cap on the IPV Mini/Mini 2.