Shorter won 1 Olympic gold and 1 Olympic silver. Ryun only won a silver. One point for Shorter.
Ryun broke world records in the 880, 1500, and mile (twice). I believe Ryun's 880 WR converted to a WR in the 800. By contrast, Shorter never had a WR in any major event. Other dudes-- Derek Clayton, Ron Hill, Ian Thompson--were running 2:08 and 2:09s during that era, but Shorter never ran faster than 2:10:30. One point for Ryun.
Shorter had 3 T&FN #1 rankings. Ryun also had 3. Tie.
Ryun ranked in the top 10 in the world 8 times (7 in the 1,500, 1 in the 800). Shorter was in the top 10 nine times (4 in the 10,000m and 5 in the marathon). A slight win for Shorter.
Shorter would've won gold in '76 if the race had been fair.
Ryun probably would have won gold in '68 if the Olympics were at sea level. (7300 feet is REALLY high. By comparison, Denver is at only 5280 feet.) And who knows what Ryun would have done in '72 if he hadn't been tripped.
Shorter had much better performances in the Olympics, but Ryun had several world records. Reasonable people can differ.
But I will vote for Ryun. And here is the reason: It's not just that Ryun broke WRs. He utterly destroyed them. In 1966 in Berkeley, Calif., he broke the mile WR by 2.3 seconds. Only one other runner (Herb Elliot) has broken the mile WR by a greater margin. Ryun set AJRs in both the 1500 and mile in that race, and those two records still stand today.
In 1967 Ryun did even better, breaking the 1500 meter world record by 2.5 seconds. Nobody else has broken the 1500 record by such a wide margin. Not before Ryun. Not after.
At his peak, Shorter was merely the best in the world. Ryun, at his peak, was a supernova.