With either of the HDs, you won't need an amplifier because they already come with low enough impedance to drive them from your PC/Console.
For the DT770 PRO-250, you will need an amplifier(Don't know which one) as I have a sound card that have a built in amplifier but others may recommend you some.
NOW, to your question, I tried the DT770 PRO-80, DT770 PRO-250, DT990 PRO-250, HD558, I chose the DT770 PRO-250.
DT770 PRO-80: Have A lot of BASS and get distorted at high volumes(for me at least maybe because it doesn't match my amplifier).
DT990 PRO-250: Just amazing. However, I returned them because they are OPEN and the treble was just way too much for me in some trance female vocal songs.
HD 558: Good sounding but I didn't like the bass at all as I listen to soundtracks and things like (2 Steps from hell) plus I like BASS so I returned them.
DT770 PRO-250: Just perfect. Closed(good isolation), Comfortable, the BASS is gorgeous, sound stage is really decent, and did I say perfect ?
Again, This is just me and my sound preference.
I just wanted to share my experience with you as I had the same problems like you.
But I also have a decent sound card with decent amp so that matters.
if you care, I bought the Creative Sound Blaster Z for $120 from Amazon that provide you with good sound quality and other features like SBX SURROUND and add to that a built in amplifier.
Thanks, hope I helped.
Edited by SKilleT - 3/1/13 at 10:25am