I've used GH for years, but tried a few other things along the way. I'm currently using Flora nova, and have been very happy for the last year with it. I didn't see any difference between the nova, the 3 part, or the maxi when I tried it, other then price. Maxi is alot cheaper, but honestly I didn't like having to mix it.
By far the best nutrients I've ever used were call Envy. I received a few quarts as samples a few years ago, and they produced the best harvests I've ever had. Sadly I can't get the product locally to me, and I don't order grow supplies online soooo I've never got to run it again. A grower friend of mine in OH is supposed to by me some gallons the next time he gets some, but we'll see if that happens. Anyway Envy is awesome, the plants love it, its a really simple 2 part that I didn't need to run anything else with when I used it. Its very cost effective, at about 9 cents per mixed gallon, as opposed to I believe GH is about 12 cents. It leaves no salt build ups in the res, pots or equipment. Long story short I loved Envy nutes, and so do the others that have tried them at my recommendation. Heres link, you can thank me later.
http://www.envybrand.com/index.php?option=com_content&view=article&id=70&Itemid=80