HELP.....WHich one would be better

I know This is not a very concise post but;
I cant decide between the:
Lenovo IdeaPad Y560 - Core i7-720QM - 4GB RAM - ATI Mobility Radeon HD 5730
$949
or

MSI GX640-098US- Intel Core i5 M430- 4 GB RAM - ATI Mobility Radeon 5850
$1090
or

G51JX-X3 - Intel Core i5-430M - 4GB RAM - NVidia GTS 360M
$1050

This Question has probably been asked before but id appreciate all the help i can get.....Thank you

one more thing....i was thinking i could get the lenovo and then add an external gpu and up the graphic performance, but i didn't know how that worked...do they work like a SLI or CRossfire....or is it something different all together