I like
ebay because-
1- easier to find hard to find coins (but expect to pay a premuium. I know I have but what choice do I have? some of this stuff is harder to find than hens teeth!)
2- get a fair market price,
3- auctions, I would say, generally 90% of the time get you the best price.
4- as others have said, if you have the patience, and you miss an auction or outbid, if you stalk, you will find another chance to bid.
so yes
ebay is nice.
now that said,, sometimes, I dont want to wait for an auction so I go with an online coin shop.