@DJ You can always stop down a fast (wide aperture) lens. You cannot make a slow lens faster. If you're ok with the added weight and cost of having faster lenses (the weight isn't such an issue for wide and ultra-wide lenses) there's no reason not to buy the fastest lens. One never knows when they're going to want to shoot a fast-moving object or have a razor-thin DoF.

As to a lens recommendation, you need to suggest a price range and style of shooting. Yes, you can replace your kit lens with a better "walking around lens" but that may or may not be what you need. I use a 70-200 most of the time because I tend to shoot sporting events, for instance.