I really don't know why this topic continues to live in the DL forum. Bin space etiquette has been debated here for years.

If you have only one bag, you get to put it in the overhead. It defies logic that someone who packs small should be penalized by being forced to put their back under the seat in front of them, while someone who packs the kitchen sink and takes up large amounts of bin space also gets to keep all their legroom.

Two bags... one in the overhead, and one under the seat in front of you, unless there is still space left after everyone has stowed their bags (or you're seated in a bulkhead row).