Subpanel Cables

Until your AHJ adopts the 2008 code it may be your choice. Do you have any other metal paths that will be bonded (metal plumbing?)

buffalo ny: a dream answer will be running extra low voltage lighting and telephone and intercom and cable tv even a drain-able water pipe, sink drain, and some category whatever they are up to now will modernize the garage with some usable spare pairs at least 5 years into its future. without these, the garage will be much less of a desirable destination. let's remember this is where the car sits and runs with the garage door open and back feeds the house during a power blackout thru a 12 volt inverter system. (!)

Four is the best way to go.

You need to have four if there are or are going to be any other metallic pathways linking the two buildings, such as pipes, CATV, or telephone