I have the v-tube. I recommend the kgo only second to the e-Power.
All three are great. You can't go wrong with any of them. It just depends on how important VV is to you.
Choose the e-Power over the kGo. The e-power, besides coming in 2 sizes is not disposable. You can repair it by buying a switch or any of the 3 pieces it comes in. If you get the big one, you can use a 3100mah Panasonic battery. You won't need to throw it away and
buy a $15-20 battery when it wears out, like with the kGo. It does everything a kGo does, but will cost you less in the long run.
The V-tube is a whole different animal. Apollo has the best deal on them and if the coupon code Reddit still works, it's hard to pass it up. If the stainless steel model is available, jump on it quick. It's the best deal I've ever seen on a VV PV anywhere. If you get it, don't
buy a spare battery from Apollo. They're o.k., but the 2250mah Panasonic CGR18650CH from orbtronic.com blows everything, including the AW, out of the water. And it's only $10 shipped.
So, you have to decide which you wan't, a VV or a fixed voltage. The e-Power and the V-tube are both great machines. I say get one of each.
And, both of those vendors are top notch as well.