I'll cast a vote for Aquasoil. I haven't used the other substrates you mentioned, except for plain aquarium gravel, so my vote is sort of biased. As opposed to gravel, aquasoil is very easy to plant in and looks very natural, in my opinion. It reminds me of pond silt, in tiny pellet form. It is very light, but still holds plants well, and is gentle on the stems. It is also very nutritious and my plants just love it. You dont have to worry about "charging" it with NPK beforehand, and as Hoppy mentioned, you dont have to be as strict with your fertilization. There's a little more room for error. It does lower the KH of the tank water and can possibly leach tea-colored tannins. But the tannins quickly stop leaching after a few weeks/months, and the water will stay clear. Another con regarding Aquasoil is that you cannot really replant or rescape your tank a lot. Disturbing the substrate will send a bunch of particulate/silt into the water column and make it cloudy. This too is not really a problem, because the filter will take care of the sediment, and it settles back down fairly quickly. I think the soft, clay "pellets/balls" are also safe for bottom-dwelling fish such as Corydoras, Loaches, etc. It won't damage their barbels, and I think the microorganisms that live in the dirt/substrate/soil are beneficial to them/their digestive tracts. I could be wrong, however. I'm no fish expert. But my pygmy cories are doing fine.

The only real issue I had with aquasoil is during the tank startup. Aquasoil really does leach a bunch of ammonia and organic compounds into the water. It does this for about a month. You will have to do large waterchanges every few days, as well as use mulm from a preexisting tank, zeolite in the filter, activated carbon in the filter, and plant many plants from the start. All these will reduce the problems with the initial ammonia and dissolved organic compounds that Aquasoil causes.

Even with the initial challenges of using Aquasoil, I still reccommend it. Its asthetics --color, texture, feel-- are great. It comes in 3? different colors. Its functionality and benefit to the plants are obvious to me as well. My HC grows great in the stuff.

Pricewise, I think Aquasoil is worth the investment. Yes, plain gravel/sand is cheaper and easier to find, and will grow plants fine -- but Aquasoil does have its advantages. I ordered mine from Aquarium Design Group. -- ADGShop.com They have a great price and various shipping options. They are in Houston and if you live in central to east US, their shipping would be cheapest/quickest. If you live west US, shipping from AquaForest in California would be cheapest/quickest. And they have prices on Aquasoil just as cheap as ADG.

Either way, good luck with your tank and have fun setting it up!
-Mike B-