Personally, I'd check Ace plus Hallmark or Vivid. EBay is a little too unpredictable/unregulated for my blood, and StubHub is just an expensive ticket broker dressed in peer-to-peer clothing.
Use ticket exchange if you are on the waiting list or know someone who is. Every other site is hit or miss. Sometimes you have to pay more sometimes less. I just bought some from ticketcity.
If you don't know anybody with access to Ticket Exchange, your best bet is Ebay. Wait until a couple of days before when people are really looking to unload a seat or two and maybe starting to panic.