Celbridge would be better value for money, in my opinion it is a much nicer village/town than Naas. Its still very small and rural feeling especially in the village and it is minutes from Lucan, Leixlip, Newcastle and so on.
Traffic would be similar in both towns. N7 servicing Naas and N4 servicing Celbridge. Celbridge has good transport links with Dublin with a train station in Hazelhatch.
Celbridge is also close to Maynooth and Leixlip train stations - particularly Leixlip Louisa Bridge. Naas has a better range of shops e.g. M&S (food only).
I live in Celbridge and find the people are, in general, very friendly.