Hmm very stuck between BB6, 7 and 9.
6 had the loft, the secret garden, the room 101 corridor behind the wall, the Big Brother control room in the toilet, and the wall where the diary room wall was situated was really cool

7 had the best garden (bridge to nowhere!), the house next door/prison (which were brilliant), the changing colour lounge, the insidey-outsidey-ness and the waterbed!
9 was used most to the advantage of the series plan, with the heaven and hell divide, with the bathroom and luxury bedroom being in heaven, and the kitchen and B-block being in hell. Loved how the decor on each side matched the heaven/hell thing, and the eyes on the front wall too

Even down to how the garden was slightly raised on the heaven side

And no one had a clue when the series began... I thought it was clever

Hmm time to ponder

I think I'll go with BB9