Hi!
On the rainy morning i was at Epcot for opening, I would say about 70% of the crowd went to Soarin first to ride and get FP. I would think this would hold true on a sunny day also, maybe in larger numbers. So i would suggest arriving early, and as soon as they let you in head to Soarin. I personally would jump in line and then grab a fast pass on my way out if you were so inclined. Realizing that the FP is good after the window of time on it, you could then head over to Mission Space & Test track. And then revisit Soarin at some later point, at your leisure.

But That is me!
Mike