the best version of both, in the 90s...... In a Cage. No rounds ! 30 minutes, without a knockout or a submission the result is a draw.....
I like Ruas in this one. He had the stronger kickboxing and could possibly have chopped Ken's legs out from under him. Marco had decent enough jiujitsu to fend off submissions from shamrock.
I have no idea how this Ken Shamrock myth became so popular. Just because he was in Pancrase, UFC 1 and famous in the WWF has given him this status. Ken Shamrock was a good fighter. Shogun is a killer.
I'd go for Shamrock. But I think ninja would be a different fighter if Rampage wouldn't have broken his arm. As the same time I think Shogun would be a different fighter without his knee problems.