What size and type wire should be used for 100 ft away work shop
Your voltage drop is almost the same for a 240v feeder at 100’ at a full load. 1.84% with copper and 1.91% for aluminum. I would save a few bucks and go with aluminum for a residential feeder,  code had no hard standard for voltage drop but the recommendation is 3% at the sub and 5% an the end of the branch circuit. Remember you need 4 wire , 2 hot a ground and a neutral. Since it is detached you will also need a grounding electrode. If the 50 amp GFCI panel is in the shop ok but I would not recommend a GFCI feeder from your main panel, that’s a long way to walk for trips. Keep the GFCI protection local to the shed.  The terminals on your panel and breakers are aluminum and copper compatible.