I am familiar with all 3 areas, Rathcoole would be the best - big village, a few good pubs, plenty of schools, mature area - after that Saggart, but there are a lot of new developments. Good schools and nice people (in general). Citywest is boring and there is no village, there is a new shopping centre though which is handy for shopping. I wouldn't live in Citywest, as it is beside Jobstown, but if you get a good deal it would be OK.
Traffic should be OK, but public transport is a disaster, so bear that in mind. Make sure to drive a hard bargain on rent, been a huge price drop in house prices in those areas. I certainly wouldn't pay more than 1k pm for a 3 bed semi, given the location