It is completely up to the individual.... Maybe you just really like the sound of over ear and dont like IEM, or the other way round.... But I would say that in actual sound quality, such as distortion etc. You get much better quality from IEM for much less money.
Also with over ear headphones there is always something which you have to sacrifice for example the HD650 have very good sound quality but no sub bass... Denon D2000 very good bass but not so good in other areas etc. A pair of IEM costing £100-£200 you can get excellent sound quality through the whole frequency range.
For an over ear headphone which is excellent through the whole frequency range you need to spend £400 or more for some top tier headphones HD800, LCD2, hifiman etc. So from my experience you get the best sound quality / value ratio from IEM....