To me, all of the LE interfaces are somewhat similar sounding, although I've never used the pre amps much at all in any of them. In any case, they're all within the same ball park.
About Logic: I have made the switch. Or, more accurately, am gradually making the switch.
It's different, not necessarily better or worse on the surface. However, out of the box, sound-wise, it's great! Just don't expect it to behave like Pro Tools in a number of it's functions; expect to spend some time with it to get your workflow down.
I switched because of the hardware issue with Digidesign. I'm sure many are.
To make this relevant to the original post. If you're starting from scratch and are trying to decide what digi system to buy, I would say that the Ensemble with Logic (even Express is great for beginners!) could be an excellent purchase.
Just a thought.