I'm a little unsure of what you're asking. eBay is a site unto itself and there is, as far as I know, only one which is eBay, Inc. Are you asking which is the best online auction site or are you looking for the best eBay stores/sellers on the eBay site?
Are you looking for a place to sell items or considering your own eBay storefront? Please provide more details and you will get much more informative replies from the community!
I too am a bit confused by your thread. eBay is an online auction website with storefronts for many of the sellers. If you are looking for assistance in setting up an eBay storefront, then eBay itself has some great tutorials and can walk you through the process.
If you are looking for other auction sites, just google "online auctions" and see what comes up.