reliable engine!!!

hey guys, Im looking into buying in the near future a FL or maybe a Mack, but basically im looking to see which engine will be most reliable, im looking into a late 90' to 2002 yr, not sure of the model yet, I have been told that the Detroit engine leaks tons of oil, but the 60 series is not bad some doubt its power, plenty of older drivers have told me the Caterpillar or Cummins are much better quality engine than the Detroit, my main reason into not looking into a Cat or Cummins engine is because im a bit worried of availability of parts now im seeking your advice ? please point me in the right direction