I used a mig on several projects and was pretty good at it (I thought so anyways....). I switched to a tig on my current project (going on now for 4 years now and a lot of welding). I personally find it hard to go back to mig.
personally tig is so much more flexible in terms of what you can weld. stainless, stainless to steel, aluminum, silicon bronze, etc and not even have to change gas mix. it's cleaner (no spatter, smoke all over the welding lens), you control how much filler metal to add, you can fuse metal without even adding metal, you can move metal around, etc. the ability to tack pieces together without adding metal, also makes the final weld joints look better.
the different torches and parts allows access to a lot more very hard to get to weld joints that the mig gun can't get to.
additionally, since it's much more precise, cleaning/dressing welds after goes a whole lot faster.
I probably use the tig over 95% of the time.
a water cooler is very nice. the small torch is so much easier to use compared to the larger torches. with the gas cooled, I found it very difficult to wait for the torch extra time to cool.
but that's just me. clearly a lot of people own both processes and likely use a mig a lot more than the tig.