The 630m and the 540m are basically the same cards. Performance wise all three will be more or less on par with each other. For me the DDR5 is a nice bonus for that card and would put it on my top list. The 2gb is nice...but you won't be using 1gb really with those laptops, your game settings won't be high enough to make much, if any, use of the extra ram.
However what I would look at first are the following: Price difference and keyboard/touchpad.
If the price is more or less the same and you're able to type a bit on the keyboards and get some use with the touchpad then go with the one that feels the most comfortable.