Comfortable Headphones for Long Sessions?

I currently use a pair of Ultrasone S-Logic HFI-450 headphones, which sound quite good to me, but I find them a bit uncomfortable for long sessions. My ears get a little sore and claustrophobic. I'm wondering if anyone can recommend a pair of studio cans that I can use for long periods of time without feeling like my ears are suffocating... Maybe I should switch to open backs?