Its a good question, but if you want the best results organically then fabric all day long. And here's why...
1) Using coir and perlite/soil mix fabric allows greater air flow producing more air flow to the roots, more air flow more CO2.
2) Only use fabric pots once! If you get an infestation of pests they can stay in the fabric. (Unless you really wash well).
3) Only negative is the cost of buying Pots every season!
At www.homegrownkiwi.com we don't like plastic lets get things a lot more environmentally friendly....as much as we can any way.