I tried having my mare on just MSM and I didn't see any sort of improvement at all. However, she's 26 (nearly 27) and not very creaky, but the creaks she has might be more than a younger horse (since MSM just takes care of inflammation, not the joint causing the pain like glucosamine and HA does - per my horse owning hoof trimmer).
The two things that have really worked well for my mare are Majestys Flex Wafers - Horse.com and I just got her this a few weeks ago (it's cheaper than the wafers) to try, with good results so far: Corta-FLX Flex-Force Pellets with HA - Horse.com.
I have tried having her on a supplement with more glucosamine and such in it but I didn't see any difference between the supplement with more stuff and less. I'm sure she'll probably eventually need more "good stuff" but for now, less is working great for her.