Have you demo'd them both extensively? Don't go on what other people use, only what works the best for you. If I had a mac I'd love to try out Logic. You might want to seriously consider it as well.
As for me, I've moved on from FL Studio to Ableton Live. FL allowed me to program beats super fast and the mixer was fuckawesome, but editing audio was pretty much non-existant and was holding me back (I couldn't stand switching back and forth from Audacity). So I could never stutter beats or do any kind of audio slicing/chopping. I mean, I could, but it was so backwards. I NEED to see the waveform I'm editing or I'm totally lost.
With Ableton I can record audio from any track currently playing without routing through my soundcard (which is shit). Another GREAT thing is freezing tracks. Basically turns any track into straight audio while keeping all midi and VST available to tweak (just takes a minute to switch between frozen and available). Which in turn saves a HUGE amount of CPU, once again a savior with my crap soundcard.
Find something with the features you enjoy and the workflow that makes it happen for you.
The big draw I heard about Cubase (and Logic) opposed to Live is that Live's MIDI implementation is slightly behind Cubase's. I heard this from Deadmau5, so take that with what you will. He uses FL for quick programming/sketching, Cubase for MIDI, possibly sequencing, and Ableton for his DJ sets and possibly sequencing too, I'm not positive. But once again, it's not about what other people use, only what works for you. I know some big name producers who won't upgrade from a 10 year old version of Acid or Soundforge, and some still programming on an Atari ST!
Same can be said about synths. Just because some big name guy can program the hell out of a Nord Lead doesn't mean that synth will taste right to you. Everyone has a different flavor and will be drawn to a different synth. I don't want to over-generalize, but you can make great sounds with just about any (true) synth out there.
Just get comfortable with what you own, learn it inside and out, and you'll be able to make great music.
Hope that helped