I don't really care how this goes either way, because I've got way more patches than I know what to do with (real military and airsoft), but I would recommend using iron on backing. IMO, this is the best option because it doesn't force any once to use any other means to secure the patch, and if you decide to, if you gives you a bit of extra reinforcement.
Most of my airsoft patches are iron on, but I use velcro. So, once the velcro in sewn on (not adhesive backing), I also use an iron to heat the backing on the patch to not only apply the patch to the velcro via sewing but also via heating the adhesive backing.
Most of my airsoft patches are iron on, but I use velcro. So, once the velcro in sewn on (not adhesive backing), I also use an iron to heat the backing on the patch to not only apply the patch to the velcro via sewing but also via heating the adhesive backing.