TopSpec - I had blue chip before and I only saw a noticable differance in one of my horses. TopSpec so far (touch wood) is fantastic for everything I have had on it.
Not tried Blue Chip but had good results on Top Spec, I used their Lesiuretime which is considerably cheaper. I have also used Equilibra on a different horse in the past with good results. It is also cheaper than Blue Chip but new ned wouldn't eat it ! (fussy or what ...). The Top Spec help line are the most helpful people ever and they will send you samples to try etc.