John's funk/soul/disco influenced rhythm guitar work is excellent - Another One Bites The Dust and Cool Cat are two great examples of that Nile Rodgers' type style which he plays great. On the Hot Space tour he also plays rhythm guitar on Staying Power, and it's such a shame the footage of that gig completely overlooks this. Roger can play a few basic riffs and chords, but is more limited than John.
Freddie only really plays guitar for composing though, and the only time I remember him playing guitar in live performances is on Crazy Little Thing Called Love
Rick wrote:
Don't forget Back Chat. The solo is Brian, but the rest is John.
Brian also plays one of the rhythm bits - the distorted power chords which pop up here and there. Not as prominent as the rhythm parts John plays there (arpeggios and riff), but still...