Ranked in these QuestionsQuestion Ranking
Pro Has a central package repository
A central repository provides more guarantees about the availability of the package. With requiring directly from repository urls, the entire project could potentially be taken down on a whim.
Pro Architecture independent
Jam's only a front-end package manager, the rest of your server can be on a different architecture or framework. No matter what the architecture, Jam will integrate easily with it.
Pro Provides the best AMD compatibility allowing for better asynchronous loading
Jam requires AMD (Asynchronous Module Definition), which means faster package loading, as it can be done asynchronously.
Con Forced AMD compatibility means fewer libraries
AMD is currently not as popular as CommonJS modules, which means if a library isn't supported, you'll have to deal with it yourself.