I live in Seattle. My main mileage account is with Alaska Airlines, since their hub is here and they (or their partners DL or AA) are typically the cheapest option when I go to book a flight. In total I fly domestically a handful of times a year, and internationally once every two or three years.

I'm attending a wedding later this spring and it looks like Star Alliance carriers are significantly cheaper than anything that will get me miles with AS. If I do get these tickets, I'd like to open a mileage account with one of the Star Alliance carriers so that I don't let the miles from the trip go to waste. Does it matter which airline's program I choose? If so, which one would be the best?

I anticipate flying with Star Alliance carriers no more than twice in a year, so elite benefits are irrelevant to me. I'm mostly in it for the occasional award ticket. There are two main criteria I'm looking for: relatively plentiful award ticket options when I do get enough miles, and a relatively long period of time I can be inactive without losing my miles.

Thanks in advance for any advice!

Go for UA or CO. The best programs if you fly only once in a while and then mainly in Y.