I've used both my iPhone (first gen, before I lost it) and my Blackberry Bold. I would recommend the iPhone and not the Blackberry. I got GREAT battery life on my iPhone (approx 30 hours playtime I think) and really only charged it about once a week. The iPod software was really nice, as long as you don't mind syncing with iTunes. The sound was pretty good too, imho - though apparently the new versions are much better.
The Blackberry was another story. The sound quality was OK, though it suffered from pretty severe bass roll off. The media player software is pretty subpar, and eats the battery like crazy. I can just barely get through the day listening to music at work (around 6 hours), a phone call or two and occasionally surfing the web on break and have 10-15% left on the battery at the end of the day. On the plus side, I'm not tied to iTunes and can drag and drop from any computer/operating system.
I'm thinking about getting the new iPhone to replace my Blackberry and Cowon S9. I'm not thrilled about being tied to the Apple ecosystem, but as an all in one solution the iPhone seems tough to beat.