Action will be your preference. Some people like a fast rod for longer casting while some prefer the extra bend in the rod which makes for a more entertaining fight.
Here is a site I had looked at before and it explains some of the advantages and disadvantages. The best way to figure out what you actually want would be to go somewhere you can try a couple out and see what you like best.
http://www.flyfishinggear.info/buyer...ods_guide.shtm