1.
Big Brother 5 - As others have said, perfect line-up of housemates, not one dull character. Brilliant twists and tasks that were all thought through beforehand and pulled off correctly.
2.
Big Brother 3 - A series that proved a relatively normal bunch of housemates can make an entertaining series. Some great tasks too.
3.
Big Brother 2 - It was the first series I watched so it's kind of special. I loved most of the housemates, especially Brian and Bubble..oh and Dean. Just a nice bunch of people who were genuinely funny.
4.
Big Brother 6 - Not a great series, but a very good series. Science and Makosi made the show for me. Most of the housemates were horrible people but it made for good viewing, Science beating Maxwell in the eviction..I think the most tense I've ever felt on an eviction night...so sweet.
5.
Big Brother 7 - Again not great, but alright. First few weeks were really good. Nikki, Aisleyne and Grace been the stand out characters. Richard was also pretty funny. But some over-the-top twists and pathetic tasks made this series a bit of a joke. But for the entertainment it did provide it tops itself over BB4 and BB8. (Didn't watch BB1 so can't judge that)
Worst Big Brother goes to BB8 though.
Oh and I haven't counted CBB, I just don't like judging it against the normal series for some reason. CBB4 was brilliant though.