Also open style headphones can be designed to have a lot flatter frequency response than closed style. But they bleed into your mics, which is why they aren't so popular for tracking.
I have both the 7506's and the 280 pros. Here's my comparison:
I think they are in the same family as far as sound goes - both have somewhat hyped high frequencies, which is not always a bad thing when tracking.
The differences are: the Sony's are a bit more comfortable to wear for extended periods of time. The Sennheisers really squeeze the head, so while that makes them less comfortable, it also gives a little better isolation. Where the Sennheiser's big advantage seems to be is in build quality. The Sony's are a little flimsy. And over time (years), the outer material on the ear cups starts to deteriorate a bit.
Theyre around the same price. I've bought probably a dozen Sony 7506's over the last decade, but after adding a Sennheiser 280 pro into the bunch, I think now i'd lean towards getting the Sennheisers, if only for the sturdier build.