What are the differences between these telephoto lenses?

I'm still a beginner at photography.
I've been playing & practicing with my 18-55mm lens for a long time and now I'm fully aware of its limitations and want to get myself a telephoto lens.

I have a Nikon d3100.

I'm looking for a telephoto lens for a price less than $200.
I have narrowed it down to following choices on amazon.

Choice #1: Sigma 70-300mm f/4-5.6 DG Macro Telephoto Zoom Lens for Nikon SLR Cameras
http://www.amazon.com/...000A0UHXU/

Choice #2: Sigma 70-300mm f/4-5.6 SLD DG Macro Lens with built in motor for Nikon Digital SLR Cameras
http://www.amazon.com/...0012X43P2/

Choice #3: Sigma 70-300mm f/4-5.6 DG APO Macro Motorized Telephoto Zoom Lens for Nikon SLR Cameras
http://www.amazon.com/...0012X61U2/

Which is better?

Added (1). I forgot to put choice #4
Tamron AF 70-300mm f/4.0-5.6 Di LD Macro Zoom Lens with Built In Motor for Nikon Digital SLR
http://www.amazon.com/...0012UUP02/

Generally Sigma is considered a slightly better lens than Tamron lenses

While generic lenses like those you mentioned can perform well optically in many cases, what you are paying for when buying a Nikkor lens for its longevity. It is not unusual for Nikkor lens to last for three or four decades. Generic lenses start to fail (auto-focus and auto-aperture) with in about 10 years. If you are a heavy user of the lens (shooting sporting events two or three times a week, the failure can be sooner if you use generic or so called third-party lenses, except for maybe Tokina brand lenses

If you do not have the time to save your pennies for the Nikkor AF-S 70-300 mm VR lens, then you need to visit a proper camera shop and hold the Sigma and Tamron lenses in your hands, attach them to your camera and try them out. This will at least show you which one of them focus faster and feels the most substantial.

None of these are great lenses as you can probably tell by the price but I would say the Sigma is better than the Tamron.

You do however need the lenses with the built in motor in order for it to auto focus on your camera.

All 3 of the Sigmas look to be the same lens. Between the 4 lenses, I would go for the least expensive, they are all going to provide similar performance.

Without going to any link, the three Sigma's seem to be the same lens but to be absolutely safe, choose between #2 and #3 because of the explicitly indicated motor included. You would need that to autofocus the lens with your D3100. Ignore the Tamron.