Newbridge is a nice town with good transport links, excellent shopping, good schools, a decent arts centre, GAA clubs etc.
Kilcullen is a nice (if a little over-developed) village with not much in it in terms of shopping or facilities. I suspect if you were to move to Kilcullen you would spend a lot of time in Naas/Newbridge.
I'm from newbridge and have to agree there is alot of advantages to moving there, although it is getting very busy, very hard to find parking and the traffic going through the town is terrible..
Depending on what estate's you are looking at as there are some rough ones (then again you have them in most towns eh) if you want all the ammenities close to you then newbridge is definaltly the choice for you..
If you'd prefer a little less and have to pop into the car and travel for shopping etc then go for kilcullen
BTW if you are thinking of any estates and would like an opinion on them feel free to PM me and i'll give you an honest opinion about them