I have in-ear molds, and headphones. Here's why I prefer the phones.
Apart from comparable isolation, better fidelity, and lower cost using headphones, the convenience and durability is far superior to that of in-ears (not to be confused with ear-buds of the iPod variety.) True in-ears require more than a few seconds to properly insert, or to remove. This becomes an instant detriment as soon as you try to have an acoustic conversation. With phones, you simply lift one earcup up, and you can hear. Same goes for feedback or volume issues. With in-ears, you have to fumble for the volume or find the plug and pull it. With phones, it takes a half second to reach up and pop them off your head.
Also, real in-ear molds need to be re-fitted periodically as you grow. This is especially true for younger users. But phones are phones... now, and 5, and 10 years from now. At worst you'd need to replace the ear-pads.
And, here's the big one, if you have a problem with in-ears, the repair process may take days or weeks, and may involve taking new impressions (of your ear canal.) With phones - any kind of phones - you can have a replacement pair in your hands within a day.
In terms of the mix, better isolation yields a better mix. With less outside sounds to deal with, the mix is easier to work with, so playing becomes easier. In most cases, a good mix is not just about what you hear... but also about what you don't hear. With iso phones, both of those aspects are more controllable.
Bermuda