The MVP2 is less powerful but tried and reliable--and accurate. And a more powerful version (MVP3) with Evolv DNA chipset is about to be released. May be worth a wait.
Eleaf iStick is widely inaccurate and temperamental--and it's still a gamble--it may last or may die within weeks. I'd wait for version 2.
I bought an MVP earlier in the year and kept it for about a month before I resold it. The eGo connector and location of the fire button were the first things I didn't like. I haven't seen anything about the MVP3, but hopefully it will have a 510 connection.
Thousands & thousands of isticks have been sold. There are maybe a handful having problems on the eleaf thread. I haven't heard anyone, that owns one, say they wouldn't buy another.
I bought 2 iSticks. I LOVE the small form factor. One of my co-workers who only uses mechs tried my blue iStick last week and thought it hit harder than his mech with a fully charged battery. I ended up giving it to him.
It might be good to compare specs of the MVP2 vs iStick.
MVP2.0
eGo connector
2600 mah battery
Variable Voltage:3.3 – 5.0
VariableWattage: 6.0 – 11.0W
Fires down to .8 ohm
Passthrough / Vape While Charging Technology
ON/OFF battery switch: 10 seconds cutoff:
Size : 23*41*107mm
iStick
510 connector
2200mAh battery
Variable Voltage: 3.3 – 5.5 volts
Variable Wattage: Up to 20W
Fires 1ohm to 3ohm
Passthrough / Vape While Charging Technology
ON/OFF battery switch: 10 seconds cutoff
Size: 75mm*21mm*32.8mm