Currently I'm a big fan of Tiny XP (Rev 09) it does everthing I want with no bloat, and has the SATA drivers included to install on my laptop.
I then just layer on the apps I want afterwards, starting with an AV and malware scan just to be sure the OS is sound.
I have tried Vista, to slow on my laptop, and Ubuntu, loved this but it had some graphics issues and the other half kept killing the wireless (not sure how worked flawlessly for me).
So a vote for XP from me, with Tiny being my preference.
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