Keep in mind that probably none of the US airlines fly to all those European destinations. So if things like in-flight experience are important to you, you not only have to evalutate an airline, you have to evaluate its partners.

I'm not sure whether by "OSL Scandinavia" you means just OSL or various places in Scandinavia. If the latter, SAS (in Star Alliance, and thus UA and US now and CO soon) has much much of Norway/Denmark/Sweden sown up to itself, while FInnair (in OneWorld, and thus AA) has much of Finland sown up. AA's OneWorld partner BA will get you to OSL (via LHR) but OneWorld can't get you anywhere else in Norway. (Which is why I collect miles "on the ground" with multiple airlines in different alliances, even if I pursue elite status with only one.! Then, at least on award trip on an airline that's not my primary, I can most of the benefits of status and more by simply booking Business Class awards to Europe.)

And keep in mind that you can't upgrade on alliances in most cases. (You can theoretically do that on Star Alliance from high fares, but good luck finding someone based in the US who's actually managed to get it to happen for them.)

Btw, you are concerned with in-flight expience, but I don't think you explained what of fares you're going to buying. That makes a huge difference in in-flight experience, because on int'l flights the biggest difference in in-flight expereince is between cabins on the same airline much more than between airlines for the same cabin, and thus the in-flight experience may depend on whether you can get into at least Business Class.

But some ailrines (AA) let you upgrade with miles into int'l Business Class from any fares with a co-pay (which you don't pay unless your upgrade clears), while others force you to buy high-priced fares just to qualify for the upgrade (and you have to pay for that high-priced fare class whether your upgrade clears or not).

Also, some airlines allow you to earn miles way faster through off-line activities (like singing up for credit cards over and over again ) than others. That sort stuff can make 500-mile minimums irrelevant to "spendable"miles. If you're concerned OTOH about 500-mile minimums for elite-qualifying miles, keep in mind that some ailrines (like Delta) regularly run promotions for earning elite-qualifying miles "on the ground" (car rentals and such), and if you can use a couple of those a year, you'll net a few thousand Delta MQMs which may be much signficant than the MQMs you lost on a few short flights. (You didn't explain how many of your flights will be short enough for the 500-mile minimum to matter. Certainly not SFO to the east coast, and I'm not even sure about FLL/MIA to JFK or IAD.)

Meanwhile, all the legacy airlines you're looking at (including Alaska) make mileage expriation trivial through either online malls and/or dining programs, which are ways to make your normal spending "on the ground" earns you some miles periodically (and earning some miles periodically is all you need to keep miles from expriing). So I don't see why you're worrying about expiration policies as any deciding factor. IMHO you should just pick an airline/alliance on factors you can't "work around" as easily as you can expiration.