All of them. I can't decide.

I voted for Season 5. Although Seasons 1 and 3 are close seconds.

All are good by voted for 6 ,don't know why.

Btw it is my favourite tv show of all times

they are literally all the same

I like this last one, season 7.
I like the old ones of course, but I enjoy the characters in the new seasons much better. I've gotten used to them. And at least in this one, House and Cuddy actually start having a real (well, as real as they can get) relationship.
I admit it's turning into a bit of a soap opera lately. It seems the only not completely messed up characters are Foreman and Wilson. Given, they have their issues, but at least their not impregnating women left and right or destroying houses. =P