In terms of Fukkery, it doesn't get better than 9. That season is a hot trashy clusterfk from start to finish. The drama is A+ but don't go into it looking for good gameplay. The first half of BB20 is a nonstop thrill ride, but you can stop watching after Bayleigh's boot.
If you want a good balance of drama, mess and gameplay BB10 is the one, BB11 to a lesser extent. BB3 & 6 are two of the best seasons. My personal favorite is BB5. BB4 is a decent watch too, but it's sandwiched between 2 superior seasons.
All of the seasons have their merits but you can skip 14, 16, 19, 21 and 22. Go into 15 with caution. There's good gameplay there, but it's so racist and toxic; there's a reason no one from that season has ever returned.
I don't recommend BB2 if you're new to the series. I LOVED it at the time, but it is slower-paced and the strategy isn't too exciting overall, but there is still fkry from the likes of Shannon, Hardy, Nicole and Will. Monica is one of the most memorable characters.