I think for an ambitious actor it is more interesting to play multi-layered characters with dark and light sides and a lot of grey in between. However, Christopher Tietjens who is his favourite character is a good man through and through. Difficult at times, impatient with fools, but with a big heart. 
But on the whole I think that the good-but guys are the real challenge. Benedict always manages to find and show the human sides and weaknesses even in unlikeable characters (e.g. Bernard in "Small Island") which he does really beautifully. 
I do not really like his Paul Marshall in "Atonement". Not because he is such a horrible character but because he is just bad. Benedict does bad really well but there is nothing for him to discover in this character. 

His character  in Stuart A Life Backwards isn't really colourful at all.

What exactly do you associate with "badass"? Because to be honest, I personally don't think that he has played many real badass roles. Khan isn't pure badass, either, in my opinion. Smaug probably is the most badass of all, come to think of it. And characters like Assange... well, those just are the most interesting, I suppose, and I don't really think that they did cast him for that role because they were thinking about his badass potential.
In his recent films, "12 years...", AOC, TIG there doesn't seem to be much badass potential, either.
So I would say, no, I don't have the impression that directors associate him with badass more than they did in the past.

I think Benedict's filmography's fantastic. He does have an affinity for prolific characters and characters that are written with depth. IMDb even quotes him as 'often portraying upper class figures' and 'usually plays highly intelligent and gifted characters'. It helps that he doesn't exactly have physical features of the archetypal good guy, as Martin Freeman does. And I think he was wise from the beginning to avoid being typecasted by choosing a wide variety of roles. 

SusiGo wrote:

Tbh, I think Paul Marshall is his most badass character.

Oh yes, I completely forgot about Marshall. He is badass to a certain extent, but I associate some other terms with him, as well, maybe even more than badass. I think he's really repellent, slimy, loathsome... okay, in the end that probably means he's badass. 

Marshall was a slimy one. I wouldn't call him badass.. imo.Smaug and Khan deserve the badass title more.

I also enjoyed watching him as Peter Guillam (but then again, is there anything I didn't enjoy watching him in?). That scene in the archive vault was the most nerve wracking five minutes of the film for me! 

Yes. He can show so much in about one minute and without a word being spoken. 

And that is what brilliant acting is all about. Inhabiting another persona completely.