It depends.
If it's a desirable name, and it's a "must have at all costs", then it's likely to be picked up by SnapNames/NameJet/Pool, then you should backorder it at all 3. GoDaddy have to compete with those 3 when the domain actually drops. they are not competitive at the drop.
If it's not a particularly desirable name, and it's not a "must have at any cost" domain, you might want to take the risk of running the gauntlet of tasters. Assuming the big 3 don't go after the domain (and you can judge that by whether anyone has backordered it at those 3), it's still quite likely that a taster will grab the domain before GoDaddy. They might taste and drop the domain several times before it eventually drops. A GoDaddy backorder will capture the domain when it eventually drops. But you could do that for yourself manually, if you have the time.
In summary. If it's a "must have" domain, you should place a backorder at all three, SnapNames/NameJet/Pool. If it's not so important, and you are prepared to take some element of riskin getting the domain, a GoDaddy backorder would be cheaper, and doing it manually would be cheaper still.