IMO, the kGo is better than the Joye (or other) eGo. The reason is the voltage they supply to your carto/atty.
Most eGos are regulated at 3.4 volts. kGos provide 3.7 volts. Some kGos provide 4.2 Volts straight off the charger, only declining to 3.7V after some hours of use. kGos also cost less, generally. kGos don't come with the poor performing tank systems of several of the eGo models (eGo-T, eGo-C).
If you get just the batteries, there is nothing wrong with the eGos besides the lower power output, which may or may not be noticeable depending on what you're using for your
juice delivery system. The worst thing about eGos is their insistence on selling you their "tank systems", which are junk compared to the alternatives, like the Vivi Novas or Stardusts. In the end, they are disposable, All the eGos/kGos/Rivas/Vgo/tGos/*Gos and now, the Twist, are disposable batteries. What do you expect from a disposable battery?
Whether it's worth it to buy a Provari over something else depends on how much money you have. It costs 3-4 x more than a Lavatube. Is it 3-4X better? IMO, not really. Is it much better? In some ways yes; in some ways, no. Both do their jobs just fine. Both have pros and cons. Both are better than the kGo or eGo or any disposable PV. Considering you can get a Vtube for $10-20 more than a kGo, eGo or Twist, and for less than some eGo-T kits, it's definitely a better value.
In the end, you can't really make direct comparisons between a $50-75 Lavatube and a $180-200+ Provari. I wouldn't jump straight into a $200 VV. You could end up being like Adam there and find out you'd just as soon have a really nice 3.7V device. You can get one helluva nice 3.7V PV for < $150-200.
Speaking of the Vivi Nova V2, I bet you will love it. I bought one and liked it so much, I ordered 2 more. The next night, the V2.5 was available, so I just had to get one of those. I think the only real noticeable difference will be the long wicks and the crack-resistant plastic tanks. I think the short wicks work fine and you can always re-wick and re-coil them for pennies. It's almost simple enough for the blind and arthritic vaper to do.
IMO, the best of the smaller clearomizers is the Fluxomizer Supreme XL from Gotvapes. Unlike all the other CE2s I've tried, they don't leak, the plastic doesn't crack and they wick well with the 70%VG juice I use. Plus, they last forever. I can't seem to burn one out.