If you get a store you will be paying a monthly fee to eBay. If you list items for auction, you pay as you go.
My advice is if you have a website of your own where you sell products, it would be a good idea to have a store on eBay as well. The reason for this is simple. Get an eBay store and you have instant traffic. Once someone buys from your eBay store you have a customer. You can then direct that new customer over to your website for more offers or specials you may have. All in all, its extra money in your pocket.