Suffice it to say there are a LOT of opinions on the matter. And there are some good scientific papers on the topic as well. You can Google it and find some good stuff out there. In fact, just yesterday Big Indiana Bass posted another of his looks at fluorocarbon from a scientific perspective. Worth a read, as well as his previous posts on the matter.
But braid and FC are two different animals, obviously. Braid is limp, FC is not. Braid is "fabric/fiber" wound, FC is "not". Braid is solid color, FC is not. Etc...
Braid is excellent for mainline using a leader of whatever for various fishing purposes. This is my approach, and I have found it works best for me on my spinning gear (and I have it on my BC gear as well). This way, should you opt for it, you can buy a spool of expensive FC and it will last a long time since you'll only be tying on leaders, not spooling your entire reel with the stuff. The braid mainline will last and last and last...
As for sensitivity, there's debate all over the board here, and it's mostly around personal experience for those of us who get foggy-eyed when the science equations start dropping over refraction indexes and such. For me, I do think FC is probably the most responsive for slack line as skeletor said; however, I've had no problems with my braid+leader for this. Here's a key here, if water conditions are right (light winds, low waves, calm) the braid reveals the slightest twitches telling me something's hitting my line. I'm using 10lb Power Pro, too, so it really moves/jerks if my terminal end is getting sniffed by a fish. In rough conditions, FC is probably better than braid+leader. But again, that's debatable.
If money is an issue, don't break the bank on FC thinking it will make you the best fisherman out there. Much of that depends on you, your style, etc. Heck, there are people who have used mono their entire fishing lives and out caught all of us combined. Would they have done better with FC? Ha, therein lies the question, eh?
So just my .02. I've got spools of FC that sit around because I'm simply not using them. I didn't find them more advantageous over my P-Line Floroclear, Yo-Zuri Hybrid lines enough to switch out.