Your best bet would be to try both of them. It's not always the best to go with the more popular choice with these sort of things. You may not like it, Ableton's pretty expensive and if you don't like it, you're out the cost of it. Try some demos of both and see which you like better.
Ableton is very complex and might take a while to figure out a smooth way to operate it but it's amazingly versatile. There are some things that FL does better but not many, and if you want to make stuff live, Ableton is a much better choice in that regard since it's built around doing stuff on the fly.
The best option is to use both of them. Figure out the best way to do things you want and use the best tools for it, there's no requirement to stick to just one tool/piece of software. I have always used Ableton myself but a friend of mine used FL studio before so talking to him I've had a chance to compare the two.
