As my join date shows, I joined D Spy's forums during bb5. Since I've always spent most of my time in the BB forum, that's also when I came here. I looked briefly during bb4 but I was happy enough in the C4 forum and didn't join here.
I'm not sure what made me switch, but one major factor was the the C4 site's forum software was
terrible, at least by bb5. It was a major pain to use. The forum software was much better here. Also, especially starting with bb7, the moderation there seemed quite random. They didn't seem to have enough disk space and threads vanished for mysterious reasons. (I know of one mysterious

vanishing here, btw, the 'Operation Aisleyne' thread.)
However, I didn't think this was the better forum overall. It wasn't until bb7 that I thought this place was better overall, and that's because, though it was very unpleasant here, it was even worse there. Even then, some of the best and most insightful posts came from the c4 forum, and quite a few of my favourite posters here had been regulars on the C4 one during bb6. Also, the C4 forum's Live Update Threads were often better that our WHATMs (more factual and including more of what happend, with less opinion that didn't say what it was actually about).
I disagree with
SG-1 about some points. In some cases, it may just be that we noticed or remembered different things.
I agree that it "got really nasty during bb7", but I think there were more bans then than during bb8. Some ill feeling from bb7 continues to this day, though it's been less often overtly expressed of late.
Still, how bad the forum seems can depend a lot on which discussions you get involved in. So from my point of view, "whole chiggy appreciation/hate situation" did not seem to create serious problems. But by then, I'd decided I'd rather not spend much time discussing HMs I liked, except in appreciation threads. (The discussions outside ATs, or "debates" as some like to call them, were repetitive and unpleasant and seldom produced any new insights.) I liked Chanelle, but there was so little common ground with those who disliked her that I mostly just didn't bother. I didn't especially like her AT either, however, so I mostly talked about other things.
And though I've always disliked Jade, I never felt much like discussing her either. So I missed most of the nastiness about her. The time I saw the most people with questionable agendas was when there was a wave of new anti-Science posters during bb6.
I thought the forum was at its worst when it was used as part of an attempt to get Jodie Marsh outside BB, especially by getting a bullying charity to drop her.
My favourite experiences here have been in the Sam (bb6) appreciation thread, and the ones for Steph in bb9 (lots of fun) and Shabby in bb11. I don't much like the chatty threads, however, which keeps me out of ATs for some HMs I like. (Not all ATs are chatty.)
Unlike
SG-1, I don't think the quality of threads has been better this year or that it feels like it's getting back to the days -- did they ever exist? -- when we could debate without getting personal.
Like
SG-1, I find that I enjoy the show more when I watch without using the forum, but I've never been able to stick it out for a whole series.