I started out by having the hylagan shots in my left knee, which is a series of 5 weekly shots and at first, had them every year to year 1/2 (never hurt once). After 5 years, the Dr. did the Orthovisc - series of 3 shots in both knees and they didn't do anything so needless to say, I had the left knee replaced at 45 yrs old. Six months after the left was replaced, I had the right knee scoped (cartlidge cleaned up) and I haven't had one single problem with either knees since. I would replace it again in a second. I notice my back and leg pain decreased significantly and my posture is much better because now I'm not walking at the "lean" to try and keep pain down.
The biggest difference I've heard and experienced personally is trust and faith in the surgeon that is doing the work. I've been with my surgeon for over 30 yrs now and I told him he wasn't allowed to retire until the other knee needs done (which hopefully now the really bad one is better, I won't need to).
Best of Luck whatever you decide.
PS: The best advice I was given by people that have had their knees replaced was to work extra hard at the excersises you do immediately after. The more you do and longer you do them, the more movement you get back and the quicker it all heals.