Normalize is practically indispensable. It takes care of many little bugs between browsers but still leaves the natural functionality of the browser in place. Resets like Eric Meyer’s “Reset CSS” make a big mess of CSS and remove all basic styling, it’s just not a good thing to do project time wise or load time wise.
Bootstrap has a lot of CSS it uses which can be heavy, but if you’re using LESS it’s easier to get what you want and then strip out the rest.
The 960 Grid System is also very helpful if implemented correctly. If you’re designing for a CMS then you can create templates for the clients and they can more easily format content when they have no prior experience with HTML and CSS.
It all depends on what your project is, but I would highly suggest Normalize and the 960 Grid System for every one if possible. I’ve built sites for companies all over the world and believe me it has saved me much frustration at times. lol