I can't say that I have seen an actual comparison between the two, but in my opinion I like the Blackberry News Feeds a lot better than the Social Feeds or any other free RSS reader (and I have tried a lot of them).
So far the only thing I don't like about the News Feeds is that when integrated into my messages folder, it doesn't mark the items as read/deleted in the actual reader itself. So I still have to go into the reader to mark/delete items. Another thing is it only offers sound alerts without any kind of visual notification on the home screen. So I just keep it on my home screen, otherwise I forget about it and am left searching for a reason as to why my LED light is flashing. LOL
On the plus side, I can actually mark items as read and/or delete them altogether, which is not something Social Feeds will do. I can't be for certain, but I imagine that allowing the messages to pile up is taking up unnecessary memory just due to that fact alone.
In the end I opted to go with News Feeds and deleted the Social Feeds altogether as I found it rather useless myself. But after trying a number of RSS feed readers, the News Feeds is still by far the best one I have found that doesn't require you to pay for it.
Hope this helps