Need Suggestion for a Fast, Snappy, OS.

I have a legacy PC running on a 1.6Ghz dual core processor and 512MB of DDR2 RAM. It has been fairly seamlessly running a watered down version of windows XP so far.

The system is used primarily to play media (720p tops).

I am looking to replace the OS and looking for something that is fast, snappy and lightweight.

I have ubuntu installed on a few systems and it does not seem particularly lightweight and frankly, Windows 8 seems to be doing a fantastic job. I am happy with Win7 too, but not too sure how W7 and W8 or Ubuntu would fare on a system with these specs.

I am open to pretty much anything, Any suggestions?

P.S. :I can handle a bit of tech. So custom/lite versions of OSes are fairly up my alley too.

Thank you!