When i started tinkering with cars, 1/2" was the one I was always looking for. Only foreign jobs used MM.
I'm not even sure if Jeeps use metric sockets or not, but I always use metric sockets on my Jeep and it seems just fine.
Personally I can't stand with I encounter bolts that aren't metric... I wish the U.S. would have gotten on board with the metric thing a long time ago.
Metric, and let's not forget Torx.
The only thing I use my standard set is my 1980 Cub Cadet garden tractor.