Depends if you count Arran as part of Ayrshire doesn't it seeing as it's covered by North Ayrshire council? Had I had that question then I reckon I would have gone for Goat Fell.
My real pet hate are questions like these in pub quizzes. We had one not too long ago about 'in which Scottish county would you find Prestwick Airport?'. Define county in Scotland futha mucka. When you look at the English county system then the closest thing we have are regions (Strathclyde, Grampian etc) but other folk (particularly English quiz masters up here) seem to think that council areas are counties.
For example, there's no way you could look at, say East Renfrewshire or 'City of Aberdeen' in the same definition as Cornwall or Cumbria.
P.S. their answer for the Prestwick one was 'South Ayrshire' but under a county equivalent I reckon it should have been Strathclyde
(Cue the usual 'Strathclyde' doesn't exist bullshit even though you still have Strathclyde Police, Strathclyde Fire & Rescue etc...)