They serve fairly different purposes, so it highly depends. In general, I find reddit to meme/joke infested (a few subreddits moderate this out, but the vast majority doesn't or doesn't keep up), but it's obviously the more appropriate format for non-questions or questions requiring discussion.
There is a lot to be said for a traditional forum.
I prefer a subreddit because stackexchange usually has too many silly rules that attract the "bureaucrats at heart". These people are more about malicious compliance and less about topic at hand.
I prefer a newsgroup/Google Group over either of those.