Depends on what you want for your mod. If you want it to support a lot of different wire types, the IPV is better, if you want it to be really easy to use the SnowWolf is better.
Officially the SnowWolf only supports nickle
coils. It can run other TC
coils, but you have to do the math adjustments and alter your temperature settings for the different wire type yourself. It won't be accurate with anything other than nickle. It's greatest advantage is it's ease of use.
The IPV supports pretty much every wire type and has upgradable firmware, but it also has a much more complicated user interface. If you can get around jumping through all of the menu hoops every time you change
coils then it's the most versatile of the two.