From our experiences last week, splash was the first to run out, then indy, then buzz then space mountain. Space was pretty calm, usually 10-20 minutes and only a few times did it get to 30-35 minutes.
Remeber with splash you can do single riders. Many times though we found the FP line for space wasn't worth it as the 10-20 minute wait is actually inside the docking station and the FP line merges outside so you may save 5-10 minutes at most. The splash FP line is worth it. For buzz, if the doesn't have 100+ people waiting outside it's not worth it as they merge just as you enter the building.
Star tours probably had the least wait for FP. 1-3 minutes when it was a 15-20 minute standby wait. For DCA, soaring then tower of terror. FP for soaring would save you 10-20 minutes but you still will wait 10 minutes in the FP line or a bit longer. TofT FP was worthless unless alladin just got out and then it may be worth it, but 80% of the time FP bought you 1-2 minutes is all.
The water ride though may only cut 5-10 minutes, single rider is the best option for this ride, as with screaming (1-3 minute waits for those two rides as single rider). Don't forget malaboomer has a single rider line either.