My personal experience is that while hyalgan worked for me, synvisc was not as good.
After the first of three injections, I felt as if I had no knee which meant I had no knee pain (whoo hoo!).
After the second, the pain came back a bit.
After the third it was right back to the way it was at first.
But...I do have to say that the pain comes and goes, so I'd like to think that when it goes it's because of the synvisc. My doc says though that since I had synvisc my insurance probably won't 'go for' hylgan for a while - six months or so.