They are three very different areas, so depends on what you are looking for. One of our relatives lived in Newcastle for the last 40 years and loved it. Couple of shops and a pub. All that has changed and the developments mostly all seem to be in the one area, there are way too many. Many of the old neighbours now want out. It reminds me as to what happened in new Lucan, except at least when the vast estates were built in Lucan there was a demand for them. Newcastle Lyons is out of balance with Newcastle, one Estate will probably have more houses than the rest of the village put together. To me, that defeats the purpose of moving to a small village.
Saggart too has its fair share of developments, but I do not think it has suffered as bad as Newcastle, or else they are better spaced.
Both of these would be an ok commute to city centre.
Ardclough would not have much development (if any) going on.