Superflex definately. Cortaflex didnt do anything when I tried it on a stiff horse. Whereas Superflex has even made my non-stiff horses SO flexible and full of life again! I have 4 horses on it..... going to cost me a fortune! Well worth it though, fabulous stuff.
I have been using Cortaflex which I have been buying for £45 for a 4 month supply from an ebay seller (who happened to be in the same town as me so delivered for free!)
However my last tub stated "not to be fed to ruminants as protein derived from mammalian sources". For personal ethical reasons I am not happy to feed my horse Cortaflex anymore because of this - and please do not shout me down for this (the previous tubs did not mention the protein source).
Having contacted Naf they advised that the protein is derived from by-products of the shellfish industry. Teamed with the experiences I have read my horse will be moving onto Superflex.
So anyone found any cheap sources - preferably online!