I run 20-25, if you are just doing steel you can run a argon Co2 blend, it will save you some coin and actually helps penetration with steel but steel only. Thing is Co2 cools the processes so a lot of people's weld suffer until they learn to crank it up a little when using a Co2 blend with a TIG, be warned though it takes a lot more practice to get a good weld with a Co2 blend and a TIG, it causes more consumption of your tungsten as well. If you are doing Aluminum (works on steel as well) you can run some Helium to save some coin, but if you do remember Helium causes a hotter weld, so you have to turn down the heat. I have not run Helium for a long time, so the prices of gas may be totally different now.