Actually I think I prefer the very first image. Some noise is ok. You subs are a bit too short to capture enough colour signal. Am I right in reading that you are capturing 20 seconds for each sub? If so this image is good for so little exposure time. Might I suggest doing 5 minutes for each sub, that will give better signal strength and over whelm background noise. You will only need to use iso 800 at most too, which will also work better with regard to noise.
Flats are important too as Trevor has mentioned. Do some sky flats just after sunset. Dust motes can be most annoying.
Keep at it.
