What do you hope to gain using a social bookmark site?
If you are looking to have remote access to your bookmarks, there are other options such as Google bookmarks or even a Firefox extension called Foxmarks. Of course in order to make use of this feature you would need to use Firefox.
Otherwise...I have only used del.icio.us and it was simple and easy to use. But if you are looking to get others to frequently browse your bookmarks...good luck! there are millions who use these services and it is easy to get lost in the shuffle.
If you are looking to make recommendations, I suggest Stumbleupon.com. It has an easy to use toolbar that makes bookmarking very easy and straight forward. Also you can discover some great sites along the way...some you never knew existed.
