I think each service has its strengths. From what I've seen of CraigsList, epecially in smaller markets, is that it's well-suited to selling old, offbeat and lower-priced odds-and-ends to a local market. If you're looking for that semi-vintage hardtail frame to build your SS project, that's the place to go.
If you want to get every whacko on four continents to e-mail you scammy offers for your bike, put it on PinkBike.
If you want a serious trading environment where most buyers understand the buyer/seller protection advantages to a PayPal transaction, then ebay is the place.
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Originally Posted by Mark Twain
"Don't argue with stupid people; they will drag you down to their level and then beat you with experience."