Naas is a great town. There's plenty of facilities for both adults and children. It's hard to say which is the best end of town, as Naas seems to be spreading in all directions, there are some really nice estates on all sides. There are no major 'bad' areas in my opinion.
Probably in terms of facilities, and general buzz, the Dublin end of the town is good. This would include the Blessington Road, Dublin Road, Sallins road areas.
The schools, GAA club, shops are all pretty accessible from these areas.
However I wouldn't like to write off any area in Naas. It is a very accessible town, easy enough to get around. There are some really nice older, more mature estates, and equally lots of newer estates to choose from.
Naas is pricey though, you pay for the central location I guess. A 3 bed could cost you anything from €340,000 upwards.
Some of the more mature estates are now selling 3 beds for about 300,000 and definitely worth a look. eg: Lakelands, Ashgrove, Monread, Roseville.