At the risk of getting a bunch of thumbs down, between the choices you have specifically asked, I am going to throw in with the .co.

I think the issue is going to be how you promote the site, where you host it and where you get your links from.

If you host it in the USA and build a solid local link building campaign no one is going to have any trouble figuring out where you should be relevant. least of all the major search engines.

The other concern would be when someone tries to type in your url directly. However, There will be a tendency to automatically add an "m" to the end. But will that be any more of a problem then trying to get people to put a hyphen in the right place?

If people really find your site helpful, they'll just bookmark it in my experience.