If you are concentrating on the UI then JQuery is definitely the way to go. There are many reasons for me to say this. I have many years experience with many js libraries. JQuery is a lot simpler to use than any the others. It is very easy to learn and it protects you from the common browser version issues that have bugged us for years.
Furthermore, it is actively supported by Microsoft. It is included in the latest web templates for ASP.NET MVC projects and there is a very active community with many innovative solutions. In short, it is here to stay.
Personally, I have found that with JQuery I can realistically write the same scripts in fewer than half the lines of code than any other library.
The main thing that it offers, which should be quite helpful to you, is the ability to add client side behaviour to one or more DOM elements at once. It does this by focusing on identifying groups of those elements in a similar way that CSS styles are applied to groups of elements. You could think of it as CSS for Behaviour if you like.
I would recommend the following book to help you on your way... JQuery In Action