In the early weeks when they actually showed more of conversations which weren't restricted to people bitching. There was a bunch of stuff with her and Bradley discussing all sorts of things from politics to science. She seemed quite switched on. Although various house mates like Angie and Josh were discouraging that sort of discussion because they had nothing to ad and didn't like that coming out.
I think you're judging more the maturity of age and social intelligence. Also, although for some reason people here like to rubbish it. You need a certain level of intelligence to be doing a Law Degree. It's all reading, writing, comprehension and logic.
Michael is a "genius", but has no time of day for anyone who thinks different or would question him.
Ben is very switched on but I think it's age and social intelligence.
The Rest, Ray had to be quite intelligent. Bradley seems switched on, but there's something off there. I don't like to judge.. too much. However why hasn't he got any goal, plans ambitions beyond continuing to work at his folks supermarket? Not necessarily anything wrong with that. It's just curious and doesn't fit. Makes me wonder if he just has a good general knowledge for his age. Although from some of his conversations with Estelle, they clearly both have gone out of their way to learn about some stuff you wouldn't normally pick up.
The rest, I don't think any have displayed really any intelligence.