I like the news much better on HN, the comments better on Slashdot. I think HN has more informative comments, but the ones on Slashdot are generally more entertaining... (or at least they were before the beta change caused so many old timers to jump ship...).
I appreciate that hacker news is kept relatively free of trolls, but sometimes it goes a bit too far in my opinion. On occasion, a very clever troll can be quite funny, and there were some hilarious trolls on Slashdot...not so much anymore.
Sometimes I feel a bit of forced fake positivity on HN. People thinking they might get startup points or something if they say the right thing. Which I guess is understandable, but I enjoy a cynical funny from a smart person from time to time.
I don't enjoy reading things like "well PG says short comments are stupid....". Which kind of slavish kiddie crap neither enlightens nor amuses me.
Bottom line, I like both sites but HN is better.