Well, unless you are park hopping - in which case I would save my FP+ for the afternoon/night park, getting an FP+ doesn't hurt anything. Both parks, Epcot and HS, are tiered so you can't get an FP+ for both rides in the same park. I would get an FP+ for the ride I am either going to hit second or the one I definitely want to do a second time. In both parks, the two rides are at opposite sides of the park, so when you go to one at rope drop, the other will have plenty of time to form a line. In this case, I think TSM will form a long line faster than RnRC and Soaring will form faster than TT. By the time you are done with the first ride and walk immediately over to the second, you could have a decent wait, so a FP+ for those rides might be worth it.
Also, TT and RnRC have a single rider line (SRL). If you do those rides second, you could use the SRL and, most likely, save time.. then use the FP+ later in the day to ride as a group, when the SRL will probably be longer for both rides. there's also the fact that if you have used your 3 FP+s early, you have a better chance of scoring a 4th (or more) during the rest of the day.