Help choosing Lens for Nikon d3100?

Can you help. I'm stuck between choosing a lens for my nikon d3100. I'm looking at Tamron AF 70-300mm F/4-5.6 Di LD MACRO 1:2 Lens and a Nikon AF-S DX VR Zoom-Nikkor 55-200 mm f/4-5.6 G IF-ED Lens.

The first one if you want the extra leeway on distance.

First one if you want a bit more telephoto and better macro, second one if you want autofocus and better overall image quality.

Unless you absolutely need the 300mm instead of 200mm, go for the Nikkor.

The claimed macro ability of the Tamron lens is little more than a marketing fad, and the Nikkor comes with an image stabilizer (the VR in the name of the Nikkor lens… Be aware that there's a non-VR version also, stay away from it) while the Tamron has none - that's a huge issue for a "slow" telephoto lens as these both are.
Also having a wide end of 55mm over 70mm makes the Nikkor at least somewhat more versatile.

I actually own both that Nikkor lens and the Sigma counterpart of the Tamron (identical specifications), and pretty much exclusively use the Nikkor, my Sigma hasn't been used for years now. I should sell it.

Also, unless the Tamron has an internal autofocus motor, it won't autofocus on your camera. I think it does though.

I too have a Nikon D3100, and I love it, and I too wasn't sure about what lens to get. I chose to get the Tamron lens, as I would benefit from the zoom as I tend to do a lot of wildlife.

Depending on what you do you would sway between the factors of zoom. The Tamron will posses more zoom, and so will be more helpful when taking photos of animals, sport and in general far away objects. But be careful! The 70mm part on a digital camera becomes larger, so this will not be any good for wide angle (but you might have the 18-55mm kit lens for that).

If you have an unsteady hand, you might want the Nikon VR lens, and that will do wide angle but the macro on the Tamron is very good, and if you find the Tamron unsteady put it on Continuous shooting, and the second or third image should be still.

My opinion on the Tamron is overall very good, and would recommend it as a starting lens (of which it sound like you are looking for), but remember the points about the Nikon, because I have tried that and I enjoy that as well, and the lens will be better quality (it's Nikon!), but once again I recommend the Tamron highly.