I went from HD555 first to DT880/250Ohm. Definitely a HUGE step forward. Then I bought DT150/250Ohm. And from that time on, I only listen to DT150. Has everything I missed listening to DT880: bass kick (but not too much IMO), more mids and good highs. In my opinion highs are better on DT880, also bass seems to go a little deeper but I missed the bass kick and more mids and DT150 provides enough of that and highs are still much better than HD555. My personal opinion and I'm definitely far from PRO listener!
My current setup:
Beyerdynamic DT150/250, Beyerdynamic DT880/250, Sennheiser HD555
LittleDot MKIII, 6N6P-I power, Mullard M8083 driver
EMU0202 USB used as DAC
Foobar 2000 on my Asus EEE900 (listening mostly to CDs ripped to FLAC)
Music taste: rock, hard rock, and a little bit of everything else