I was referring to public transport TB. The Airporter is the quickest way from BFS-Derry (unless you spend £50-60 on a taxi). Average fare is £28 rtn. If you land at the airport between Airporters, you can either wait up to 1.5 hours for the next one, or you can spend £10 rtn into Belfast city centre, which can take anything up to 40 minutes depending on time of day, then £17 rtn on a Goldliner to Derry (1 hr 50 minutes).
From BHD, £3 rtn from airport to Europa (tkes about 15 minutes), buses every 30 minutes to Derry (often more frequent at peak times), paying £17 rtn on the Goldliner.
I've driven BFS to Derry in little under an hour. At the same time, I've taken nearly 2 hours during Friday rush hour.