I am new to container gardening and wish to plants various hardy perennials in large containers and leave them out all year long. My question is: what kind of soil should I use? Potting soil, garden soil, my own awful clay soil or a mix of all the above? Would greatly appreciate any thought on this, as I am now starting to pot em up!
Your soil is the most important choice you'll make in establishing your container garden, so if you concentrate your efforts on learning what separates a good soil from the pack, you'll be taking a significant forward step in your quest for results you'll be satisfied with. The article Pirl linked you to will help you understand the soil/aeration/watering relationship, which is probably the source of more problems in container culture than any other aspect.
Buy pine bark that looks like what you see at 3, 6 or 9 o'clock below. Use 5 parts of it mixed with 1 part sphagnum peat and 1 part perlite. Add 1 tbsp dolomitic (garden) lime to each gallon of soil.
The concepts highlighted in the thread you were linked to are really much more important than the recipe. If I had to distill everything into a sentence, it would be that you can't build a highly aerated soil that supports very little perched water by starting with a large fraction of fine ingredients (like peat/compost/coir/topsoil/sand); you must start with a large fraction (75%+) of large particulates (like the pine bark you see below) in order to reap the benefits from superlative aeration and little or no perched water.