I had the great pleasure this week in eating at both of these great OC sushi places this week. I've noticed that there seems to be a pseudo-rivalry between devotees of the two restaurants here on Chowhound. In fact, I've been a long-time customer of Sushi Wasabi, and just had to get down to Shibucho on the advice of all the hounds here.
After trying both places, I can definitely see why one people will strongly prefer one of the places to the other. The philosophies behind their omakase styles seem to be so fundamental. Sushi Wasabi has tended to stick with more or less a fixed omakase set, with variety coming in only in terms of availability. SW also tends to focus more on milder tasting fish. This was especially obvious to me tonight at Shibucho, where I suddenly realized that I've never been served saba or uni at the SW omakase before.
Also, SW seems to focus more on giving you a good quantity of high-quality fish, while SS seems to be more concerned with giving you a variety of what is available. SW will give out at least two pieces of everything (excluding the rolls) while the only thing that I remember having two of at SS was the anago, and even that was served with two different kinds of seasoning.
Having tried them both, I think I understand why many people here have such a strong preference for place over the other. It's not simply a matter of quality, since both restaurants do serve very good sushi. It's more a matter of what style of omakase you prefer.
I think all in all, I think SW is a better choice for relative newcomers to sushi, due to it's emphasis on high quality ingredients, the overall flow of the meal, and it's preference for milder flavors. SS seems to be a better choice for experienced sushi-fan, with more emphasis brought towards the difference between the different flavors that each piece has to offer.
These are just my thoughts on the matter, with everything still fresh in my mind. I'd love to hear everyone else's take on the issue.