I agree with trying both, but with a twist. I would sign up for a platinum challenge on American, and then I would fly nothing but American until the challenge was completed (go to the American forum, and read the sticky at the top of the page about challenges). I am under the impression that UA will match status, but you might inquire on the United forum about that. If you could get a match, you would then have status in both programs. You should compare flying with status on American to flying with status on United. You will be doing a lot of flying, so you will have status on whatever airline you finally choose. If you spend 6 months flying both airlines, I would think one of them would stand out for your needs. I would definitely try then to put as much business on your preferred airline as possible, unless you will be flying enough to make top tier on both.