Avoid the v2 like the plague. Because it used a specialized tool that LOOKED like an allen key, but was keyed into a triangle. The metal on said tool was of poor quality - felt like tempered aluminum and had a tendency to round off / snap at the slightest torque. MXv3 all the way - it comes with the standard MX style drip tip, a 510 drip tip adapter, and has phillips head screws in it. Which means no special tool, can practically use anything you want to tighten it, and it just feels of better quality than the v2. The v4 - I would suggest that if you aren't worried about a bit of juice leaking and aren't prone to crushing barrels (as the v4 barrel has been thinned out quite a bit). Although both my v4's leak very little - I've seen them leak profusely. Most of the leaking seen in the v4 comes from the O-rings that secure the barrel to the deck. The bottom airflow is a nice addition, just understand that if you ARE going to use the bottom airflow, you can't just go ape.... and drip juice into the atty. You need to paint your coils and wicks with the juice. If you just drip directly into the atty onto the deck, you run into the issue of juice pouring out of the bottom holes. Honestly - it's your juice and your choice...