My ranking used to be reversed, since the first Genesis album I owned was Seconds Out, which has live versions of both songs. The piano intro to "Firth of Fifth" was only played live a few times and is not present here. Meanwhile, "The Cinema Show" has that awesome instrumental with Collins and Bruford on drums, and it builds up to a big climax. Pretty mind-blowing stuff right there.
Then I picked up Selling England by the Pound and discovered that "Firth" has that piano intro, plus the first E minor solo is played on the flute. Meanwhile, "The Cinema Show" doesn't build at the end, but rather fizzles down into a segue back to the album opener, which is well done but disappointing in general after knowing the live version first.