One day in and the Beyerdynamic T90 is an amazing headphone. Was hard to stop listening to it last night. Whilst the Grados remain a top notch headphone too, they are very different with a super clear and clean presentation and highly charged rhythmical nature but a more closed in and punchy soundstage. The Beyerdynamics are smoother with a much wider soundstage and more instruments identifyable. It is still clear and detailed but less punchy. Bass is excellent on both, there are more layers to the treble on the Beyerdynamics.
At the moment the Beyerdynamics are winning but its early days, they are definately more comfortable, do not leave your ears slightly exhausted after an album like the Grados can. I do prefer the wider and less tiring experience, but there are times i would expect to want to listen to the Grados too.
Either headphones are highly recommended by my ears. Will continue to try them out alongside each other over the coming weeks.