Ok, obviously I haven't ridden either coaster yet, but when I created this thread, SW8 looked small and disappointing on the plans and whilst I felt that Merlin's marketing team would ensure the largest increase in visitors,I also felt that Icon would be by far the better ride.
Against all the odds, it looks to be coming down to the wire. It looks like we have a great thrill coaster and a great family thrill coaster with amazing theming and effects (if they maintain them).
I think both parks have done well and I wish them every success. I think that WM looks as though it may justify the "World Class Experience" claim, though apart from a lot of digging, I don't see where the "groundbreaking" claim comes in.
Will be a while before I get to ride them both, but really looking forward to it. At this stage, I'm expecting two excellent, but very different coasters, but I suspect that King Nemesis will retain it's crown.
Won't know for sure until I've ridden them.