Which of these Nikon lenses are better in general?

Nikon AF 70-300/4.0-5.6 G Black Nikkor Lens - http://www.amazon.co.uk/...00005Y3OM/

or

Tamron AF 70-300mm F4-5.6 Di LD Macro 1:2 Nikon+Motor - http://www.amazon.co.uk/...0012UUP02/

I have the Nikon D3100 but I only have the kit lens (18-55mm VR). What I'd like to know, is which of those lenses are better in general? My gut instinct goes for the Nikon one as it's VR, but I'm really clueless! Also, is 70-300mm focal length good? I'm assuming it is, but I want to be sure.

First of all, the bigger the focal lense the further away you can be to take a picture. I recommend the Nikon AF 70-300. Both have their merits and seem to be good lenses and seem pretty similar anyways.

The Nikon.

Although the Tamron claims to be a "Macro", at 1:2 is not really a macro lens.

VR is very helpful to beginners.

The nikon you posted is a predecessor of the current lens( which is here: http://www.amazon.co.uk/...000HJPK2C) it's the 70-300 G also known as the g-type. It was a kit lens for the double zoom kit F55 film camera at the end of the film era. For film which was typically not printed very big it was good enough.
I've owned that lens. Let's say the 100 quid is about right for that lens. If you're not too demanding and you have good light you can shoot a decent pic with it. And I shot with that lens. It DOES NOT autofocus on a D3100.

The tamron is a slightly updated version of the lens I tested a few years ago. Performance is about on par with the nikon but at least you get autofocus. Don't expect much from the "macro" function and you will not be disappointed.

If you're looking for a general allround lens to zoom in just a bit more and have no real plans to do wildlife or birds then this would deserve a good look: http://www.amazon.co.uk/...B000O161X0 It's nikon's 55-200 Vr. It's stabilized and autofocusses on your camera. If you insist on 300mm but can't afford nikon's 70-300 VR then this is an accetable alternative: http://www.amazon.co.uk/...B003ZSHNCC
Both lenses are decent optical performers and easily among the very best at that price point.

I've been trough 3 dirt cheap telezooms before I bought the nikon 70-300VR. It's not cheap but in my opinion it's the best 70-300 ever made for nikon and probably the best sub-400 tele option you can find for a D3100.

Nikon and Tamron make some good 70-300mm lens, but the cheap models you are looking at are not the good ones. If your budget won't stretch to the better 70-300mm's, get the Nikon 55-200mm AF-S VR. Although 200mm is less than 300mm, you can capture more detail with the better image quality.

The Nikon 70-300mm VR lens is targeted towards sports, nature and wildlife photographers that need a lightweight, versatile telephoto lens with great optics and vibration reduction technology, at an affordable price. The lens works on both Nikon FX (full-frame) and DX (cropped) sensors and has an equivalent field of view of approximately 105-450mm on DX sensors, which makes the lens particularly good for reaching distant subjects.