Hubski was the very first aggregator I encountered so I have no experience with Reddit (except what I learned from Reddit's creepy kiddy porn guy (now banned) when he was interviewed on CNN.) The people on Hubski seem open to new ideas, arguments, respectful of differences and willing to learn (mostly). People seem human, fun, and funny.
Some cool Hubsi features (that I appreciate):
If you post a comment, it's easy to go back and edit it if necessary.
Everything is saved and easy to find.
mk is open to ideas even if they appear in a dream
and generates lots of new ideas himself.
I can send people here without being worried that they'll be offended by really stupid, immature nonsense or comments.
But Cortez - it takes a while to get a feel for the community. So lurk on.
About a year ago, I was sending my parents links to some great stuff on reddit. There was still some excellent discussions happening, especially about privacy online which my mom was getting really interested in. Unfortunately, after about 4 links over a couple months my mom decided to explore. She was none to pleased as the top AskReddit post at the time was regarding the weirdest porn.