What wire should I run to my garage for tools and a welder?
You probably want to run to a subpanel as that will give you a LOT more possibilities as well as allowing you to run 120 or 240 devices.  240 @ 50 amp would require 6/3, and you could actually breaker it at 55 to give you some more room.  Look into code in your area as to what kind of method is required for bringing power to an outbuilding.  In the subpanel you will need to have separate ground and neutral bars.  You can then run whatever outlets and loads you want to without going back to the main house.  6/3 at 100 feet will also not exceed the 3% voltage drop that is usually considered &quot;within tolerances&quot;.