Freelancers visa in HH?

My wife and I are planning on moving to Germany from the USA this autumn and applying for freelancer's visas — I'm a computer professional and she's a yoga teacher but we are thinking of also getting CELTA-certified to be able to teach English, to broaden our income possibilities.

I've been looking at Berlin but it seems the market is fairly flooded with English teachers (or is it?).  So I was thinking about Hamburg, where I've lived for a year long ago (wonderful city).

But when I hear of artist's/freelancer's visas I really only hear about Berlin (I have several friends in Berlin who are doing OK on artists visas). 

Is it possible to do it in Hamburg as well?  Is it harder to get a freelancer's visa there? Could we try to get freelancer's visas in Berlin, and if it didn't work out there, move to Hamburg?

Thanks for any info!