Neither is the "best". It's all preference. Try them both and see which one you like more.
That said, I find jQuery much easier to use for simple things like you mention. Prototype is more "advanced", so to speak, and takes longer to master (and you will probably never use 90% of it).
Like musicfreak said, neither is best. It all depends on your needs, ability and style of programming. Both will do what you wish, but but the style of the backend code is really different between the two libraries. My best suggestion is to look through their tutorials and documentation and see which one you are drawn more to. If you don't like the syntax of one library, go with the other. Also, be sure to look at examples and the examples' source, they will usually give you a measure for how involved and skilled you need to be to pull off the tasks you are going to try.
To the extends of my research, I do "BET" JQuery would became the most popular one, the reason I say I am betting becoz once you really dig into one technology, you always hope it become the best :P
The reason why I vote for JQuery is simply the support from those big shots. Like google, like also ASP.net MVC is actually INCLUDING JQ in the beginner's template. For me, I like coding in ASP and C# and also using MVC with JQuery is much more comfortable than with the traditional ASP.net and AJAX Framework.
In terms of functionality, I think they (Prototype, JQ, or even Mootools and so on) could provide more or less similar for you, say DOM manipulation, event binding, the browser-independent abstraction layer. So the framework itself I can say, they are in par. For plugins, maybe you should go and check out the exisiting plugins that whether they can achieve what you want. JQuery does have loads of plugins that I think they should be enough to help all those usual task, and it is really much easier than you can imagine to author a brand new plugin on top of it.
One last thing, no matter prototype and JQuery is not actually OOP tools, neither nor Javascript itself. It does work in objects, but not exactly in OOP way (like lacking direct inheritance and class encapsulation). And you might take a look at JQuery.inheritance plugin that actually do that.
*Final words to add, if you plan to develop on Palm Pre and WebOS, then go for Prototype... Coz they are shipping the device with prototype preinstalled.