All three cameras are excellent images makers. If you can find a good deal on the NEX-5, then swoop it up. But, if I was buying now I would buy the 5N. The new sensor looks to be really amazing and it can take the optional EVF. I think those two things are worth the extra price.
Between the NEX-5 and the C3, I would take the 5. It should be cheaper now and it's not that much worse specified - in fact better at some points, like the 1080i-movie-recording. And, in my opinion, the handling is much better, but that's down to a personal preference.
If money isn't that much of an object for you and if it's not much more than 200 USD more expensive than the NEX-5, get the NEX-5N. You'll quickly appreciate it's faster autofocus and more future proof specifications, not to forget the new Sensor, which is better in low light. The touchscreen is just a toy, for that matter, but well, we all like toys, don't we?
You really should hold both cameras and check out the ergonomics. A lot of people like the squarish grip of the 5 and 5N. I originally bought both the 3 and 5, and kept the 3, because I felt like the 3's flatter but wider grip fit my long and skinny fingers better. I recently bought the 5N, and was reminded of why I didn't like the grip of the 5. So I'm returning the 5N, even though the IQ is slightly better than the 3 (and 5).
I feel feel the NEX get a bit of bad press regarding not having quick access to main commands like iso etc. I find that the custom button setup is great. really pleased and a great companion for my Nikon D3100.