Hmmm, OK… so probably my recommendation would be either Backbone or Knockout. I’m slightly biased here, as these are the two frameworks/libraries that I’ve had most exposure to, but I’ll explain my reasoning:
Small learning curve: Backbone is relatively simple to get your head around, and sticks close to the traditional way of working with the DOM. Knockout is maybe slightly more complex due to using two-way data bindings and making you declare those bindings directly in the HTML.
No need for additional tooling: Both will run by including the relevant scripts in your page. There’s no need for additional build/compile steps, or setting up task runners etc if you’d prefer not to.
Work fine with or without jQuery: Both will happily co-exist with/use jQuery out of the box, although Knockout doesn’t need it to function and Backbone can be configured to work without it if you’d prefer to use native DOM methods.
Good support/community: As both have been around for a long time now, there is good documentation, plenty of articles and tutorials available, and many plugins/snippets for doing pretty much anything you might want.
In terms of pros/cons for choosing between them, Knockout is really just a view library and leaves you on your own in terms of application structure. Backbone, on the other hand, provides other components like models, collections, and routers.