I'm glad the question was "Who's your favourite whistle-player ?" and not "who's the best ?", which is a ridiculous question. Based on playing Irish and Scottish music on whistle for over 30 years, here's my answers.
The best example of whistle playing I ever heard was by Finbar Furey, playing a solo at the Thurso Folk Festival in 1977. He played the slow air "Lament For Oliver Goldsmith", [by accordionist Seamus Shannon ], and followed it with "The High Reel". As near to perfection as it's possible to get.
The best recording of whistle-playing, in my opinion, is still Mary Bergin's first recording, "Feadog Stain". I would say that 3 other Irish recordings come very close, and all 3 I believe would have been influenced greatly by Mary's playing. They are the solo CDs by Brian Hughes, Vinnie Kilduff,and Gavin Whelan. Other notables with individual styles might include Desi Wilkinson, Sean Ryan, Brian Finnegan, Carmel Gunning and Cormac Breathnach, and all 3 of the Smyths – Sean [ of "Lunasa" ], and his sisters Breda and Cora.
Brid O'Donoghue, from Co. Clare is about to release her first CD in the next week or so, and I believe it will be up to the standard of any of the recordings mentioned above. Look out for it.
Sadly, as far as I know at the present time, there has only ever been one recording of Scottish solo whistle playing, and that was by Alex Green a few years ago. One recent recording which has some excellent whistle playing of both Scottish and Irish tunes, is by Julie Fowlis, who is also an extremely fine singer of Gaelic songs.
If you absolutely insist on only one favourite, I'd have to choose Mary Bergin.