I am a Nikon D3100 user. My kit lens is the 18-55mm and I also have 50mm. I'm thinking of buyig tamron 18-200mm OR 70-300mm because that's the only brand that suits my budget. I am into portrait photography at the same time I also love doing event photography. Since I live in a province from the Philippines, near the forest at slightly in a higher level land, when I try to do nature or landscape photography, it makes me look for longer mm. Because our place is almost at the higher level than the city, moon, stars and even birds are slightly reachable that's why I wanted to also try wildlife photography. I wonder what lens should I buy that fits to my lifestyle ? The 18-200mm or the 70-300mm? And also, what lens is best suits for candid photos especially for children? Because I also have so many nieces and nephews..
The 70-300mm VR is a good all-around lens. I've used it throughout its range. If you're at the beach, in an open park, or just anywhere really where you have enough space between you and your subject (at least 5 meters), then the lens will work well for portraits of all sorts & candid shots. You can also stitch together panoramas somewhere between 70 and 100mm (or longer if you want), and you can get some creative shots.
I've posted three photos below. The last one is a 70mm candid full body portrait with the 70-300mm vr.
Here's why you might want to consider the 18-200:
The first two photos I chose just because I took the shots from a similar spot on the beach, pointed in a similar direction. The wide shot was taken about 1 hour after the telephoto shot, and the wide shot was taken about 20 meters back from where I took the telephoto shot. Look into the distance (down at the very last most distant tree on the wide shot). You can see the mountains in the background just past that tree. Now look at the telephoto shot: Same mountains. While this doesn't illustrate every possibility and every difference between an ultra wide angle and a telephoto lens, the point I'm getting at is that an 18-200 could switch between a wide angle, and a telephoto perspective. In a split second, you could switch between two different kinds of shots without moving, and without reframing.
Here's why you might want to consider the 70-300:
You get 100mm extra reach, and you get a little bit better performance for telephoto work. The 70-300 is also very snappy to focus, and it is consistent when it focuses. The difference between 200mm and 300mm can make a huuuge difference, depending on what you intend to photograph. I know that 300mm isn't enough for me most of the time, so I'm usually cropping in my photographs to get a 600mm, 900mm, or even 1200mm equivalent. If you find yourself cropping in a shot taken at 200mm and you need a 1200mm equivalent crop, you might not be totally satisfied with the results.
11mm (taken with the Sigma 10-20mm f4-5.6):
180mm (taken with the Nikon 70-300mm VR):
70mm (taken with the Nikon 70-300mm VR):