I don't think being at the extreme of either leads to happiness. People on the genius scale are often full of self doubt and over analyse everything and are never satisfied with their current situation
Likewise I imagine that being stunningly beautiful can get in the way of normal social interaction.
A good mix of both is preferable. There is a correrlation between face symmetry (proxy for beauty) and IQ anyway, I read an interesting piece in the nat geo a few years ago. Being attractive means people respond better to you and your interactions become easier.
I am quite clever. Very clever compared to the whole population I suppose. I am also reasonably attractive. I am tall, slim, nice face and nice hair. Def not stunning but I am nice looking.
I bloomed late, at about 20 I suddenly 'grew into my looks' and boy did life become a whole lot easier. Social interactions became much easier, boys wanted to talk to me, more girls did too, it was easier getting part time casual work at uni (and I was told by a guy at one job that the manager had only Interviewed be because he thought I was 'fit').
As other people have said it is well documented that being attractive makes a lot of things easier. But you don't need to be stunning, a plain face can be an attractive face if you are presented nicely and are confident and happy in yourself.
My DP is ridiculously clever. Scarily clever! He Often thinks it would be nice to be stupid and just accept life the way it is!