The Beyer DT-220 are a very solid pair of headphones and excellent for serious mixing requirements.

While the DT-100 are now the industry standard (and for good reason) I have no regrets buying 4 pairs of the DT-220 which I managed to pick up 2nd hand for £40 a pair.

The range is good at 20-20,000 htz and the sound is fairly neutral, being neither too bassy nor too trebbley.
What you hear is what you get which makes these ideal for professional jobs. I have used these for day long sessions without suffering any ear fatigue which is essential.

The only downside I've found is that out of the 4 pairs I have 2 of them had rather hard ear cushions whereas 2 pairs did not. I think that over time the cushions get slightly harder. Thankfully you can still get replacement parts for the 220's which includes new ear cushions.

In total, I would go for the DT-100 over the 220 due to the slightly increased comfort and broader freq range, however, for the money the DT-220 are more than decent for the studio professional, are of great sound quality and will also last a long time.