Fantasmic, for sure. You can go for the dinner package and not use an FP+ on it. But you have to commit to a table service dinner. Either way gets you into the reserved seating area.
Illuminations- but I scrapped my FP+ when I saw the FP+ viewing area and realized that we wouldn't be in line early enough to be by the rail for best viewing. So we found a spot at the rail about 20 min. early in WS and it was much better!
Illuminations gets our vote, if we had to choose one can't miss night time show. We would be sorry if we had to miss it b/c we didn't get a FP+. However, we agree with belledream, use FP+ for rides, you can almost always find a space to watch this Epcot jewel, totally worthy of a FP+.