It depends on what you want to shoot. We buy dslr's so we can change lenses, but it is also nice to not have to carry them or change them for a given activity. As mentioned, the 18-140 is a great walking around lens. The 18-105 is good too if you are on a budget. You could spend a day walking around and be happy with either of those lenses. Not a lot of zoom though, but good for people pics and many vacation sights. Not so good for wildlife unless they are close.
You have a 50mm, which is great for a lot of things you might see walking around. Its a bit too close for some indoor situations and not great for wide landscape. With that in mind, I vote as well for the 18-140 (or 105) so you have some wide coverage too. Get the longer zoom when you have a specific need for the reach, and then decide between the 55-300 and 70-300. The 55- is lighter, smaller, cheaper and easier to carry. The 70- is heavier, larger, more expensive and somewhat clunky to carry around, but its a better lens.