I was wondering which way is the most common way or best way to feed to a new panel. I am installing a 100 A panel in an detached garage. The feed will come from a 200 A panel in a garage that is close by. There are two ways to do this I believe...First you can run something like USE-2 in a 2-2-2-4 and the 4 can be the grounding conductor for all the circuit grounds as long as the panel does not have the neutrals and grounds bonded. The second way would be to treat it as a new service and run something like 2-2-4 and have the 4 be the grounded conductor and then start a new grounding system there with new ground rods. Which way is best? Thanks.

The 4-wire connection is the best. A main CB and a grounding electrode system is required in either case. With the three wire connection you have to worry about parallel paths on the grounding electrode system with the grounded conductor. Not a problem with the 4-wire.