I've used quite a few brands, and settled on Rio Fluoroflex Plus. It's readily available in local shops, knots extremely well, and hasn't given me any reason to switch brands. Umpqua's Super Fluorocarbon is exactly the same as Rio's Fluoroflex Plus if you can't find Rio around.
The flouroflex plus material is quite a bit more supple than previous fluorocarbons, and I'm impressed enough to use it almost exclusively. I still wouldn't want to fish a FC leader, however. I haven't encountered any problems blood knotting flourocarbon to nylon leaders of similar diameter.
It's probably not a good idea to use fluorocarbon on small dries, as it tends to drag them under, but I think it's ideal for larger, more bouyant dries, as the tippet gets right below the surface film and doesn't tend to stand out as much as nylon does (in my eyes, not necessarily the fish). Fluorocarbon is hands-down a winner for nymphing/streamers.
Obviously the knots you use will depend on the difference in diameters you're connecting and how large they are to begin with. But properly lubricated and tightened improved clinch and blood knots haven't given me any trouble. You've got to love the abrasion resistance of fluorocarbon as well.
Don't forget to dispose of it properly!