Stores generally work best if you are listing new, or very specialised and hard to come by used items. Even better is you have multiples of the new stuff.

You can have the best of both worlds if you have enough items, open a store for your new items if you can manage to utilise most of the 80 free listings and use another id for selling auction items using the 40 free listings a month.

That way your total listing fees will be twenty bucks for 120 items and you will only have FVFs to pay on top of that.