I will just give you an excerpt from my Vaper's Handbook to help you out.
Q42: Can you review some of the more popular APV/Tube Mods on the market for us?
A42: I cannot. I do not own any of these devices at this time but I can give you my assessment to the best of my abilities.
The EGO C Twist is a very inexpensive option. If you polled all the variable voltage vapers on ECF you'd find that the vast majority of them vape just above 4v. The EGO C Twist has a variable voltage range of 3.2v-4.8v . It will serve most vapers very very well. If you don't own one yet I would start here. I strongly believe that every vaper should have an EGO C Twist in their arsenal. That is why I recommend it at the beginning of this blog. (Yes I do have 2 Twists)
The KGO VV: I would avoid the passthrough option that is the KGO VV. I have seen too many horror stories of them venting/igniting while being left plugged in and unattended. IMO passthrough batteries are pretty fail because every second you plug them in and the battery is fully charged you are challenging the overcharge protection circuit and begging to damage your property. I don't know the amperage specs on the KGO VV but I highly doubt it will have what it takes to push high voltage (6v) at low resistance. Stick with a Twist in that case. If you are a reckless throat hit chaser there are better/more effective (though more expensive) options.
The Lavatube 1.0 (2.5 amp device) is not a flawless device, but it's $55 (for the tube mod only) right now (at the time of this posting) due to the fact that Volcano is releasing its Lavatube 2.0 (3 amp device) and clearing stock of the 1.0 to make room for it. There some things that suck about them though that you should know about before you buy one. They are often incorrect about the voltage you set them at versus what you actually get. They also lower the voltage (without indicating it) as a safety precaution without telling you on certain combinations of low resistance atomizers and high voltage (due to lack of amperage). This may or may not bother you. There is also a lack of proven reliability.
The Apollo V-Tube is another option. It is a 6v variable voltage device set to compete with the Lavatube 1.0. (2.5 amps, same as the Lavatube 1.0). There used to be coupons floating around the forum here to make it quite affordable. People who have them have reported that they are generally pleased with them.
The Vario (by VaporBeast) release date (as of this posting) has been pushed back for 2 months while they deal with issues that arose from the review models, but that may turn out to be a good option too (it will be a 5 amp device by far the highest so far). It will also not require an adapter to use with all the currently available atomizers on the market. With the kind of amps it pushes it will not limit you with low resistance multi-coil atomizers (as low as 1.2ohms) at high voltage. According to Ohm's Law they won't be worth vaping at full voltage at the lowest resistance it could handle (1.2 ohm) especially on a single coil it would be 30 watts OUCH - we're talking a direct line into the underworld - true volcano stuff. At 6v on a 1.2 ohm dual coil cartomizer you would get a shocking 15 watts per coil at 5 amps which is probably too hot. If you put a triple coil cartomizer at 6v, 5amps then that could be a really awesome vape at 10 watts per coil. Time will tell if this device will play a major role in this market yet but I am personally excited to watch the action unfold. If these issues aren't dealt with then the Vario will never be released. The owner of VaporBeast, Tim Campbell, refuses to release the Vario unless it is exactly to the specs on his website and working well. This is definitely not the "need it now" option.
The Vector by VaporBeast is a good APV as well. Has all the functions of a Lavatube but I believe it's 4amps which is nice. Plus it's shiny. $69 - $75 (depending on color) out the door with 2 18650s and a charger. Blows away even the Lavatube 1.0 with its big sale right now. Free Shipping.
The VMAX Ultra by Vaporbeast is also a good APV, it has 5+amps and all your standard APV functions. The LED screen is bigger than most and it looks AWESOME.. $89 out the door with 2 batteries and a charger. Free shipping. The only problem with this APV is that it's not in stock at the moment.
The Provari is very very expensive. They are often pointed to by fanboys that they have a reduced price of $160, but a quick run through the numbers on their site will reveal that you aren't getting out the door with the perfect APV (18650 batteries x2, battery cap for 18650, decent color, 1 year warranty) for anywhere near that (IIRC it was over $280 for the colors and options of your dream package). If you have the money, the only thing you can go wrong with on the Provari is the price, the fact that they require an adapter to fit certain clearomizers (like the stardust for a crappy example - this is an extra cost/possible appearance issue), and they lack the amperage to push low resistance multi-coil atomizers at high voltage (it's a 3.5 amp device) like the Vario will do if it is released and the VMAX Ultra does now (if they ever get any more in stock).