Nikon... difference between 18-135, 70-200 and 18-200?

I have a Canon camera and if I were just going by focal length, I think you can get the best bang for your buck by buying the 18-200. That way, you can get both wide angle and a zoom/macro shots. But, I would also like to know what the maximum f-stop is on the lens. The wider you can set the aperture, the better. especially if you like to shoot at night or in low-light. I wouldn't go any smaller(higher number) than a maximum aperture of f2, if I could afford it. If the 18-200 lens had a maximum aperture of, say 1.4 or 1.6, that would be an outstanding lens, but those are usually extremely expensive. I only have a fixed 50mm lens for my Canon, but with a wide-aperture and it's fantastic. I've had other lenses with my Pentax, but not with the higher apertures and they were hard to use in low-light.

You should have one main lens known as a walkaround lens. This is the lens that you will keep on your camera most of the time. It should have a pretty wide range so that it can be very versatile. As for what other lenses you'll want to purchase, you should look at your photography needs. If you shoot a lot of landscapes, you'll want a very wide angle lens. If you shoot a lot of sports or wildlife, you'll want a telephoto lens. I have a Nikon D70, and my walkaround lens is a 28-300. It's perfect! It's really all I need! The 28mm is wide enough for all of my wide angle needs, and the 300mm is long enough so that I can get really close whenever I need to! In my opinion, you're not going to find a more versatile lens! As for my other lenses, I have a 1000mm that I mostly use for astrophotography (mostly taking pictures of the moon), I have a Lensbaby 3G which is a selective focus lens I use for real creative shots, and I have a fisheye lens that I also use for creative purposes. I do plan on getting a macro lens in the near future. But for sports, wildlife, landscapes, portraits, still life, nature, and most anything else I photograph my 28-300 works perfectly fine! Nikon Nikkor lenses can be pretty pricey, so you may want to get some third party lenses with a Nikon mount. I would highly recommend Sigma lenses. I've also heard that Tamron makes excellent quality lenses as well. They are very good quality and much more affordable!