Many authors portray Akane as someone who has good acting skills, or has the interest and/or ability to become an actress. The only reason for this, that I can find, seems to be the story where Akane is keenly interested in playing Juliet. This tends to bleed into other situations in works of fan-fiction, with how she interacts with others outside of that context.
However, I was considering the story where Nabiki becomes Ranma's fiancee, and began to wonder if Nabiki made a better actress than Akane. After all, she's more expressive than a good number of authors are willing to portray her -- *Cough* Ice Queen lubbers *Cough* -- and has a lot more control over her actions than Akane does.
Ranma's not up for consideration because he's another kettle of fish entirely. There are far too many instances in which he puts on an act, and how one might gauge his ability is more likely to be skewed by irrelevant or trivial factors. Basically, he could easily be seen as being the better actress, or just as easily be seen as the worst. I think it'd make things a lot less complicated to keep it between Akane and Nabiki, though if one feels like another character (or characters) need to be addressed, you're welcome to start another topic.