I would search around your local tire places and see who is having specials on four tires. Or what i have done is gone to tire rack.com and ordered some great yokohamas and when i got them i just took them to a local shop and had them installed-saved a lot of cash!
The "best" place to buy is a subjective question and can only be answered with an opinion, not a fact.
I would suggest buying tires from Big O Tires. They guarantee their tires. If your tire blows or even goes flat by running over a nail, they will replace it if it is still under a certain amount of miles.