I saw the movie last night in IMAX 3D and again with my nephew today in regular 3D..
I'd say the IMAX 3D is a lot sharper, clearer, and brighter, so if you have an IMAX 3D option, go for it. Both are pretty good though, but with IMAX, you'll never have to worry about the screen being too dim/dark.
I said this on the other thread, but I've seen once in 2D once in 3D. Best post production convert to date, and by a wide margin. It's not Avatar, but it sure as hell isn't Clash of the Titans. You won't regret spending some of the extra money for 3D.
Don't you think you're doing a disservice to a great movie by straining to watch it in a muted version? Ex: Everything in the land of the Frost Giants was dark and you could hardly tell what was going on. Those same scenes in 2D are spectacular. IMAX offers the best of both because it wasn't as dark or unfocused. I'm telling everyone I know to watch this movie in either 2D or IMAX but avoid the Real 3D at all cost.