There was a thread on this a little while back, I think last month. I tend to believe that used as per manufacturer's recipe (to compare a full diet to a full diet) that they are all about within 5% of each other. I believe that using the manufacturer's full recipe makes the biggest difference.

The other conclusion from that thread was that when you get your environment optimized that the nutes will make the biggest difference.

Personally I use Technaflora. I've used Advanced, and botanicare.