[ASnep]

On the technical side, Sky's the best for UHD.  Apart from being live (iPlayer has the usual delay), Sky is broadcasting in Dolby Atmos, whereas iPlayer is just stereo.  The BBC's linear HD coverage is DD5.1. 

After all these years the BBC still can't offer the best audio simultaneously with the best video.

Sky's Yotube stream is 4K HDR HLG as well BTW.