First of all, its Mystic Timbers hands down. However, Orion still does have great theming.
MT essentially is built around its' theme, which is why I love it. Between the truck, que line, music, train design and shed it is a total experience.
Orion definitely has this same "experience" vibe as you walk through the lab before getting on the ride and I love it, but it doesn't measure up to MT's in my opinion. Orion is more about the coaster - and it should be!
Overall, I respect a ride that makes an effort to sell it's "theme." Not everyone feels that way but the best rides have his quality in my opinion!