Many people speak highly of Soil Master Select and have experienced really good growth with it. It may be a good option and cheaper if you can find it or alternatively you can get aquariumplants.com own substrate which is really Soil Master Select repackaged http://www.aquariumplants.com/product_p/ss-1.htm
I have experimented with Schultz Aquatic soil and fluorite, I am less than impressed. Many stem plants that I tried planting in the Schultz Aquatic Soil are doing pathetic even with c02 injection and proper ferts. These include, hygrophilia Polysperma, ambulia, Ludwiga(I tried 3 different types and they all did bad), cryptocornes, and Rotala Indica. In my experience, these plants do not seem to root well in the Schultz Aquatic Soil.
In my fluorite tank, the results are a little better but not spectacular.
Some other things that you can try are Seachem Onyx Sand. It apparently buffers the PH, but this has not caused a problem for my plants and fish yet. I have had the best results with a low tech tank using a thin layer of peat, leonardite and mulm capped with Seachem Onyx Sand. Leonardite can be really expensive and more than a bag of eco-complete or fluorite. I set this up for experimental purposes and was okay shelling out the extra cash. You may or may not want to pay the outrageous price for a small container of Leonardite considering you only will need to use a thin layer for this kind of setup. You can see the results and details of the setup here: http://azdhan.googlepages.com/thelostworld2
I have no experience with eco-complete. Whichever way you go, you will likely have to fertilize the water using something like Tom Barr's Estimative Index schedule. The amount and frequency will depend on whether you go with high tech(high light c02 injected tank) or low tech(low light and non-c02 injected tank).
P.S. Some people have also successfully setup Natural Planted tanks using regular garden topsoil capped with regular gravel or laterite capped with regular gravel. I once saw a display planted tank of a store owner who set up a high tech tank with c02 injection and the substrate was laterite capped with chicken grit, of all the things. His plants were absolutely beautiful. They were lush green, had huge leaves, and the anubias were flowering. He told me that he used no water column fertilizers at all, go figure. I found it hard to believe that plants would grow in a tank with that kind of substrate and no water column fertilizers at all, but I cannot deny what I saw with my own two beadie eyes. I saw another ladies 5 gallon hex tank that had been set up for years. No c02, she was using a cheap compact fluorescent bulb from the dollar shop for the lighting and using hagen geosubstrate black sand with no fert tabs, and no water column fertilizers. The tank was overstocked with fish that had been alive and healthy for years. And most surprising of all, the plants were growing like crazy and the rate that most people would claim would not be possible for a non co2 low tech tank. These are things that I have witnessed and seen.