I like yard sales better. Typically a better price and more variety, even though you have to drive around a bit. Certain neighborhoods have better stuff than others. Ann Arbor was always excellent.
All the cool kids are around the I75/696 area. Royal Oak, Clawson, Ferndale, Berkley, Southfield, Oak Park or Madison Heights. Everywhere else is crime-ridden ghetto or havens for tasteless rednecks.