Can you be more specific? Your query is like asking "how long is a piece of string?" or "what is the best flavor of ice cream?" What species of coins do you want to buy and what traits in a dealer are important to you?
Yup. Every dealer specializes and provides a level of customer support. Want the cheapest? May not come with any return privileges. This is what many who decry certain dealers do not understand. A coin is not priced by God. A dealer has differeing levels of costs and benefits associated with buying from them, costs that need to be recouped somehow. What you are looking for may not be what I am lookoing for, and we will be willing to pay differently based upon that.
Maybe give us an idea of what you're looking for. America coins, world coins, price range ect. I will say this much however, I've don't really well with a company called northeast numismatics.