BB9 for me. I was always entertained, the ones I disliked got their comeuppances, and the most deserving one (imo) won.
BB10, too. It was very entertaining and underrated in my opinion, one of the best ones. Wasn't a massive fan of the final 5 bar Siavash and David, though, and I didn't like some eviction results, but the series entertained me.
BB11 started off very well, but the latter half was pretty dull.