they are both good phones, but i would probably go for the E6. the u600 is slightly better on the music side, but not by much.
the E6 is faster in everything, mostly because of its much faster processor. the u600 is really slow at some things such as taking pics, opening up videos(especially if the video is large, etc), etc. it's nippy around the menu and for texting, but the processor speed is only around 87MHz, and this hurts it when it comes to the more processor intensive stuff.
the E6 is also of stronger build due to it's dimensions. the u600 is solidly built given its dimensions though.
the UI is better as it is more configurable.
in summary, the E6 is superior over the u600 except in the quality and resolution of the camera and the maximum amount of memory.
advantages of u600:
-better camera in quality and resolution
-greater maximum memory because it takes 2GB + 60MB. E6 has 2GB + 8MB
-slightly better for music if the same headphones are used. make sure that you buy yourself a 3.5mm jack and use your own headphones. the supplied ones are nothing to write home about.
advantages of E6:
-speed
-UI (more features and more configurable)
-dimensions (ie probably better if you don't treat your phones well)
-reception
-battery life is twice that of the u600 (battery life on u600 is nothing to write home about)
-3.5mm jack
-takes SD memory which is faster.
