I've put my Sony against the iPod 5.5G, iPod Touch 3G, iPhone 4 and 4s. I've come away happy that I've since gotten rid of the Apple stuff and happy with the sound out of my Sony Z. I've even built a nice LOD for it ($60 worth of parts)... and put that into an iBasso D-Zero. The sound was louder, but more like an iApple device. The sound was more linear. I like the curve the "Z" has. I like the tainted "tube" like sound. This was with the stock buds, Re-cabled UE TF-10, Sennheiser PX200-II and my Heir audio 4.A... LOVE THE SOUND of my "Z".
No doubt the Z1050 sounds better than iphone 4, just not a huge difference like I was expecting but still an improvement nonetheless. I find the Sony have more bass output and the sound range seems a bit better than my iphone 4. Very nice sounding player.