I would like to get opinions on which JS framework is best for a relatively simple website. I've looked at extjs but it seems more focused on complex webapps than a website. Important to me will be styling, autocomplete, ajax support, basic dom manip.
You DO want a rather popular framework, rather than an obscure one. Popular ones are most likely to be best debugged and regularly updated.
A lot of what I will want to do is around UI controls - auto complete, combo boxes.
I will also be doing a lot of dynamic manupilation of DOM objects - getting a list of results displaying them, sorting them, etc.
You'll find people who love each framework, and people who hate each framework. Really, it all comes down to personal preference -- take a look at the documentation for the ones that interest you, look at the sample code, and see which one fits your style of programming the best. The one that is easiest for you to work in will be the best choice for you.
What you use would be dependant on exactly what you are trying to do?