I don't like to compare, but other people do, and in this case, reviewer Adam Baruch has some, most likely, controversial things to say about Yes vs. Flash.

Of all the Progressive Rock bands that flourished in the early 1970s, British legends Flash were always among my favorites and the forty years that passed since, basically changed nothing in that respect. I always claimed that Flash was what Yes should have become: a gutsy, focused and multifaceted outfit which was able to write great music and cross genres elegantly rather than indulge in endless doodling and ego trips. No wonder that Peter Banks left Yes after a couple of albums and formed Flash with vocalist Colin Carter, bassist Ray Bennett and drummer Mike Hough (with another ex-Yes member, keyboardist Tony Kaye featured on their first album). The band managed to record three classic Prog albums, which to this day sound absolutely brilliant and are prime examples of the genre.
For the rest of the review—http://www.adambaruch.com/reviews_item.asp?item=104372