Cubase and Nuendo seem to be the pro standard at the moment.
Reaper is great for its video and post functions but not the best for working with MIDI.
FL is out of the picture, the video player is glitchy (try a tempo automation I dare you).
Studio One is actually one of the better options, I'm curious what issues are you experiencing with it in regards to video and/or syncing?
Pro Tools is currently having video issues although usually its okay. MIDI is a bit cumbersome to work with in there but theres a plus to knowing the program in some work areas.
Logic is a great alternative to cubase and the MIDI workflow is nice. Price point is a bit cheaper than cubase but cubase has more advanced functionality with scoring.
Ableton works, but nothin fancy scoring-wise.
I hear Digital Performer has some percs for scoring but I know nothing of those.
Also have heard mentioning of Samplitude for it, again Im not sure of its percs.
In summary, I'd go for either Cubase or Logic personally.