Rathangan is ten miles from Kildare town and parking in any of the train stations either in Newbridge or Kildare is difficult. You would probably get a bigger house in Rathangan than in either of the other towns. However, in my opinion there is no comparison in the locations. Rathangan is still, despite new developments, rather out of the way, and it is possible to buy, in your price range, a house in either Kildare or Newbridge within walking distance of the station.
Newbridge is the bigger town with new shopping centres and plenty of facilities and it is about 30 minutes by train to Dublin. A bus service called the Silver Dawn leaves Newbridge at about 7.20 , goes to the quays and lands in UCD at 9am.Kildare also has developments near the station but is a quieter location than Newbridge. Depends what you want, either way the commuting can be tiring, and will further travel after you get off the train be worth it for the country air?