If you will be travelling to Europe often for weekend trips, you may or may not be flying the cheaper airlines, like Easyjet. I don't think they have a ff program (unless you count using an AA or UA credit card to buy the ticket).

Most people usually pick their ff program by deciding which airlines they fly most. Is life worth connecting in AMS if you are always flying beyond AMS?

If you are seeking coach tickets and not status or upgrades, Alaska Airlines program has many partners. Other FTers may have more information about other less obvious programs, like Qantas, etc. I once redeemed an award in Lufthansa's program earned from flying United and other carriers besides LH.