/feed/ if you have activated permalinks (which you should)
I’m not sure about ‘should’, yes, activating permalinks could have it’s benefits for the end user, but I’m not sure someone has/can conclusively prove that not activating permalinks puts your site at any real disadvantage. IMHO.
Perhaps this codex page explains the location of your feeds better.
http://codex.wordpress.org/WordPress_Feeds#Finding_Your_Feed_URL
Regarding whether it’s a valid feed or not, this codex page might help.
http://codex.wordpress.org/Customizing_Feeds#Checking_Your_New_Feed
The feeds seem to be working. Thanks all.