I recently started playing around with Node for a friend's side project. I helped him set up the database and Sequelize was absolutely horrible to get up and running. The documentation was really lacking and we spent hours trying to track down little details needed to get things running. It does the job once you have it set up, but I found getting to that point was way more difficult that it should have been.

I used Sequelize for a while before Bookshelf was released and haven't used it since so I'm not sure how it compares these days. One thing I like about Bookshelf is that the query builder (Knex.js) is fairly decoupled and it's not that scary to drop down to the SQL layer. I still feel it's not quite as good as it could be.

This might not be objective because I hate sequelize but sequelize sucks! I never understood its API. Is so clunky compared to Bookshelf.js.

Bookshelf is less opinionated on the way you integrate it with your web app with makes it good to work with if you have strong opinions on how it should integrate with your codebase.