I can't do a direct comparison but maybe this will help:
I've heard the DT880 vs the T1. T1 is better overall - better detail retrieval, better bass quality, and for my ears, better midrange, and smoother highs. Was able to try them side by side, and much, much preferred the T1.
The HE-500 is very different - detail, balanced, natural. It is easily in the same league as the T1 as a product in terms of quality, and even better from a price to performance ratio. They are both keepers.
I am not talking about them being equal in technicalities, but if you talk about "great headphones" in general based on their own individual merits, the HE500 holds its own.
Go for the HE500.