There is the 84X which takes about 80 minutes to get into the city centre, and it is roughly the same in the evenings. It avoids going through Bray and Shankill. They are fairly regular in the mornings and evenings, but don't run much during the day. If you have to use the 84 to get into the city, you'd be better taking it to Bray and getting the DART from there (it does not link up well with the DARTs in Greystones).
Very few people I know drive into the city, although quite a few drive to Greystones or Bray to get the DART.