Have used both in the past and have to say I am most impressed by Topspec. I have my current horse on Topspec - he loves it and looks well on it. There has been a noticable difference to his condition since being fed Topspec.
I like blue chip. I havent tried top spec so can't compare but both of mine (tb and welsh d) look fab on bluechip, grass and haylage and have done for the last 2 years plus my tb holds her weight now which she didn't when I got her and she isn't quite insane...
I used to use Blue Chip but the price gradually went up to a ridiculous amount so i changed to baileys Lo Cal Balancer. My horses have thrived on it & about £12+ per bag cheaper than Blue Chip I'm also a lot happier.
Mine is now on Blue Chip, and changing from Original to Pro. Will give it two bags and see how she goes. She has a good coat, but has been through the mill a bit and lost a lot of weight
.
Used Topspec with last mare and she seemed fine on it, but was a diffent kettle of fish to this one.
I have feed Blue Chip to my three year old wbxcob since I got him at 15months and I have to say I am very impressed with it, his condition if fab and he is always very calm and chilled out. One bag last just under two months so well worth the money.