What are people opinions, which should I go for?
Ps sorry but my knowledge on headphones is very bad haha!
ES10 definitely. That is, if you can stand having them scratched. If you do mind that, though, then M80 is an automatic choice.
In my opinions, M80 has a slight V-shaped sound signature, but that's not to say their bass and treble are over-emphasized, but rather... that their midrange is a bit withdrawn. Maybe I'm just too used to the ES10, but midrange in the ES10 makes many headphones in the $300 range and lower feel recessed and lacking (DT880, DT990 in particular come to mind here). They also lack the big, bold, thunderous bass impact of the ES10.
In general, I think the ES10 sounds like it's a "bigger" headphone compared to the M80. But that might be just me.