I like the design of Hubpages the best. It's very easy to add new modules. I've made some very similar pages (same topic, similar titles) on both Hubpages and Squidoo, and hubpages gets WAY MORE TRAFFIC than my squidoo pages.
BUT, on pages where they are buying pages like product reviews or something, I've had MORE SALES on my Squidoo pages.
I've just started using Infobarrel, so I can't really compare them.
You can help the HubPages community highlight top quality content by ranking this answer up or down.