Windows 7 should be fine, but expect the odd issue to appear requiring driver updates, patches etc.
Vista has been out long enough to be stable and trouble free, it's just that many knock it without ever having used it. W7 should have hit the ground running eing based on Vista to such a large extent.
Buying today I think you have to go with W7
The Sony and Tosh are good brands but as with everything you can be lucky and unlucky. All manufacturers have the odd model that may develop a common fault etc over time.
I have an Acer... it's been brilliant, 3 years old, gets lots of use, excellent... but that's just my experience.
Drop any laptop and you can't "expect" it to survive unscathed ;)