Hey Redflare,
I own knives in both steels too and I can't say anything more than what Billym said. 154CM is definitely, to me, easier to sharpen but I can't say for sure which would hold an edge better. S30V is one of today's "super steels" and is supposed to have better edge retention qualitys but, the steels have to be tested side-by-side for me to confirm that and I've never done that with any knife. So I'd just have to say I'd bank on the expert's testing and believe that it'll hold an edge better than 154CM....depending on what it's asked to do, of course.

What kind of knife are you considering and what will you ask of it? Maybe then you could narrow down which one would be better for you.