Again this will depend on your use case and budget. Lenses with lower maximum apertures (more gathering capability) will generally be more expensive but perform better in lower light situations. If you want a blurry background to separate and enhance your subject, there's nothing inherently wrong with an f/11 lens; your subject just has to be far enough away from the background to make it blurry. It really helps to know what you will be shooting and under what conditions before you take the plunge and buy a lens that doesn't match your intended use.