For laptops, I look at the processor.
The 3rd laptop has the best processor, and not that much of a difference with the graphics card, 9600M is fine.
Also, the 3rd laptop has better resolution than the 4th.
However, the 3rd laptop is the most expensive, so if you want something a little cheaper, go with the 4th. If you can afford the 3rd laptop, definitely get it.