First my answer would be to try the standard Ubuntu. Your system meets the requirements.
But keep in mind that Ubuntu will probably work but quite slowly in your system.
Here is the link:
If you feel that is too slow for you my next stop would be Lubuntu. Keep in mind that this distribution is not as well polished as the standard Ubuntu.
But this consideration should be a general statement. First, if you meet minimum requirements you should try standard Ubuntu with the Live CD. If it does boot and you find it fast enought (it always takes extra time to load but after that it just works marginally slower than regular instalation without considering the time to start new apps) just keep it. If it is now good for you just look for more lightweight distributions like Lubuntu, Xubuntu, etc.
Good luck and I hope you enjoy your new system!