I've used both, and the real stuff somehow seems to feel better, although the synthetic still works fine. One advantage of real cork is that you can make it thicker once it's on the sax, using steam, to cater for a mouthpiece with a slightly larger bore than standard.
i got mine on ebay it came from the states
not sure what it cost,i think it was about £3/4 less than a fiver any way.
i have done it now and it was easy to do and it has worked a treat it stoped the leak i was getting from cork area and looks good as well
I buy cork from here too, "Saxmanjamie" in Canada. Always great service and he does other bits too, not just cork, the re-corking "kit" is complete with glue, knife and sandpaper complete with instructions that a five year old could follow.
I recently did one of mine with a self-adhesive synthetic neck cork I got from a firm called Karacha that sells stuff via Amazon and through eBay. It did a nice job! I have tried sythetic before with mixed results. It is quite springy and much more difficult to file/trim to a nice smooth edge on the join than cork is. Also, it seems to have less latitude in accepting different mouthpieces. If it is the right thickness for your neck/mouthpiecem then great, but for some set-ups it isn't thick enough. Also, it can't easily be sanded down as it tends to break up. I'd say its harder to make a nice job than with proper cork. I get all my stuff from Windcraft as a rule and keep a box of various cork, evo-stik, lighter fuel (dissolves old evo-stick), sharp blades, metal ruler, fine sandpaper, felt, PTFE taoe, heat shrink sleeving and an emery board. This also allows me to deal with situations when bits of other cork wear out or fall off my saxophones. For pads and such like, I go to the tech!