Just wait until the MVP version 3.0 hits the market, which should be within the next few weeks. It will be a marked improvement over the current 2.0, and there will be several versions with different chips, one of which will be a DNA chip built exclusively for Innokin by Evolv. All versions will feature a spring-loaded 510 connector, a better OLED display, a larger battery, an improved fire button with better placement, and the charge port will be on the side rather than on the bottom. The base version will fire up to 30W.
The iStick is also being updated, but the version 2.0 probably won't hit the shelves for at least a few months. The biggest complaints right now are about power regulation (Vavg vs. Vrms), crappy 510 threads, the center pin gets depressed, and sometimes the fire button doesn't quite make a connection, so it doesn't fire the device.
If you absolutely have to have one of these devices right now, go with the iStick. Just know that it will fire hotter than what the numbers indicate, but if you aren't a low voltage/wattage vaper, this should not affect you. The iStick hits about a volt higher than what is displayed at the lowest setting, and as you increase the voltage, the device becomes more accurate. Also, just use the included 510-eGo adapter all the time to preserve the threads and eliminate the problem of the center pin getting pushed down. You can also buy the optional bending adapter that eLeaf sells, as that includes a spring loaded pin assembly. As for the fire button not making contact every time, it only happens every so often, so it's not a huge deal. Check out pBusardo's review for a full breakdown of what to expect with the iStick -
https://www.youtube.com/watch?v=_W1G7p_fCJw
If you can wait, then hold off until the MVP 3.0 is released. It's gonna be a killer device! At the very least, you can probably snag a really good deal on a 2.0, as the sellers will want them off the shelves ASAP.
*EDIT*: Just found this - apparently, Innokin is releasing an MVP 20W, which has a flush spring loaded 510 connector. I hope this isn't the actual 3.0, though.
http://www.tasteyourjuice.com/wordpress/2014/12/04/innokin-announces-the-mvp20/