Join every airline and hotel program you can. If you are flying that much you will find great deals throughout the various programs and you never know when some miles will be beneficial. (Like the current AA 20K promo where a transfer of 10 orphan miles through Points.com from an airline frequent flyer account that you have never used, but received 500 miles for an e-mail address submission; suddenly those miles are worth 1000 miles in your AA account.)

Which program to maximize your miles in is a much more difficult decision.