I'll try to give you a break down of each. The short and quick answer is, it really all depends. Here are my thoughts:
A) This will take a long time to rank as each subdomain is considered a separate site. Folders would be better here.
B) This would be the quickest way to rank and add relevant content to your site. It just depends, does your site already rank?
C) This is a good play, but you should use AreaAKeyword.com, AreaBKeyword.com, etc...that would give you the benefit of location specific and keyword. This will take a while to rank as well as each site will be new. From an SEO stand-point these domains would be strong.
D)I'm not sure I understand this one. Are you talking about using widget.com/Area-Widgets/? That would be a good play as well.
Overall, I think you just need to figure out how much time and effort you want to put into this. Link building and overall optimization is easier for just one site. And again, it really depends on your business.