What size wire should I use to feed a subpanel in my garage?
My answer is almost always the same when talking about garage subpanels.


60 ampere double pole breaker in the main panel.
6 AWG copper wire (x4) for a run less than 75ft., 4 AWG copper wire (x4) for runs less than 150ft.
60 ampere panel with 60 ampere main breaker.


Unless you're running a whole bunch of stuff at once, a 60 amp panel should serve you well.

If you're running individual conductors, you'll definitely want to run it through conduit.  If you're using a cable assembly, you'll probably only use conduit if you have to. For example, if you have to protect the cable from physical damage, or it will be underground.