When you ask for the "best" place, do you mean the cheapest? Nicest people? Stellar return policy?
I've bought tires from a variety of places online, but only because I was living in Hawaii, and my local retailer wanted double the online price. That didn't include mounting or balancing, which I think was $50 each, if the wheels were off the bike. Back in Seattle, my local retailer wanted just a couple bucks more than online prices, and mounting/balancing was free, off the bike. In my opinion, that was the best place to buy a tire. Not only was it competitive, but it kept my local guy in business, so I could zip over and get helmets, gloves, batteries, brake pads, filters, dang near anything. Anymore, your local shop probably also has a web store as well.
If price is paramount, try looking at less expensive models. There are lots of good quality tires out there, that will serve you well, but won't break the bank. As an old friend said to me once, "I don't buy high performance tires, because I'm not high performing."
The absolute cheapest place though, is probably used tires on ebay or craigslist. There's a guy near me on CL that was advertising "hundreds" of used moto tires for free. Can't beat that!
Ah, here it is. You're welcome. LINK