I am using velcro. I am not totally happy with the situation it looks and holds alright. However, it doesnt always line up correctly and straightly. I was thinking about trying some magnets.
Much smaller the velcro. It all depends on the type of armor you are putting on and where. Chest armor made of Sintra you can use snap but you have to dremel the inside of the armor a bit to drop the snap down to make it flush.