I usually go down with a uv and a circular polarizer. I have some photo experience but far from a pro. I personally haven't found anything else that makes that big of a difference. The above two are my choices and the circular polarizer is my favorite.

A polarizing filter and circular polarizing filter do exackly the same thing. But most modern cameras require the circular to work with the built in light meter. so get the circular.
Remember to use the filter at a 90 degree angle to the sun, or it will not have an effect. Otherwise remove it as it blocks off a lot of light.

I've used a polarizing filter with limited success... mostly because I don't know what the heck I'm doing :).... but I always use a UV filter. Protects the lens and I do see improved pictures.
My two cents.
Bill