In the which Comply tip gives more isolation debate. The deeper the fit, the better the isolation. Now, this cannot happen to all people. Me, for instance, I cannot wear the standard size. They stick out to much and I get a Frankenstein complex going. It also has to do with the shape of your ear. If you have a good round ear canal a standard size will give you better isolation. If you have a smaller canal, the short size. If you have a collapsed, oval, or other "odd shaped" canal; foam, silicon, rubber, tri, biflange, etc. cannot always get the right fit. That is when a custom mold comes into play.