[Chawanwit]

I was going to buy the Q701 for $440 US when I found out that the DT 990 250 Ohmz sells for $350 US in my country. Which is a better buy for me?

 

[Dubstep Girl]

the dt 990 is better if it was the 600 ohm version. but ultimately it depends on what you listen to. both are very good headphones and in the same price/performance bracket.
 
both will require an amp and the k701 are slightly better than dt 990  when properly amped.