With optics there are all sorts of compromises. Building a relatively compact zoom with a large range generally means several tradeoffs which usually include poor image quality, especially at the extents of the zoom range, and a variable aperture that gets pretty narrow on the long end.
The 55-300 is a much different lens. The difference between 18 and 55mm is much bigger than the difference between 200 and 300mm. This may seem counterintuitive. At a fixed 15' subject distance the horizontal field of view at 18mm (for a Nikon FX DSLR) is 67 degrees. At 55mm it's less than 25 degrees. For 200 and 300mm the numbers are 6.9 and 4.6. You can see this for yourself by taking the 18-300 lens and taking pictures at all these focal lengths, then comparing the field of view. You may be surprised by the results. Rather than focal length sometimes it's better to think in terms of FOV.
I have the Niikon 18-200. The only thing I use it for is my infrared converted D5000. Not all lenses work well with infrared and the 18-200 just seems to work very well with this camera for whatever reason. The reason I don't use this lens on my other Nikon bodies is because there's just more compromises with it than I'm not willing to accept for the convenience of having such a wide focal range.
When someone asks for a lens suggestion, the first thing I ask is what kind of subjects and in what situations do you intend to photograph with it? Many amateur photographers buy a lens and then figure out what kind of subjects to take with it, but this is exactly the opposite way to go about it.
To answer your first question, the answer is no, I really don't have a zoom in that range I'm happy with and I don't think I ever would be happy with a zoom of that range. I can't really answer your second question without knowing the specifics of what you are looking for. What I can say is that when I'm looking for a single lens that will offer the greatest versatility, without question that lens is my Tamron 17-50mm f/2.8. This lens is not as good as the Nikon 17-55 f/2.8, but it's about 1/2 to 1/3rd of the price and it's still a damn good lens. It does have a few shortcomings like ergonomics and the image stabilization isn't that great, but for my money it does what I want it to do. The difference in size and weight between the Tamron and Nikon is my main consideration, not to mention the price.
So what will the 17-50mm do? First the FOV range is quite large. At the same parameters as above it covers 70 degrees at the short end and 27 degrees at the long end. This makes it a moderate wide angle and a short telephoto. You also get a f/2.8 fixed aperture which is much faster than the super zooms and image quality is going to be better across it's entire range. This lens is also pretty light which is a big consideration if you're going to be carrying it around on your camera all day. This lens works great when I'm on vacation because it does most landscape and people pictures quite well which is usually about 90% of the shots I want. With this lens I will often pair it with my Nikon 180mm f/2.8. The reason is because this lens is actually pretty light and compact for a long telephoto even though it's a Nikon pro lens that's all metal. So it's easy to carry in a backpack or some other bag and because it's built like a tank, I don't have to worry about it too much. If these are the only two lenses I have, it leaves me with a big gap between 50 and 180mm, but there's not that many shots I'd want to take that I'd miss in that range.
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