If someone else is paying for it, buy the most expensive ticket you can get away with on whichever airline gives you the most points. Since all programs are now revenue-based, this will result in the most points. (But don't just buy a last minute walkup first class fare if doing so will get you fired.)

If you are paying your own way, buy the least expensive ticket on any airline that meets your personal standards. (Schedule, no. of stops, comfort level, etc.) Keep the money you save and use it to buy more tickets later on. While this won't give you the most points, it will result in you having the most money.

If your money doesn't matter, then you really don't need to be asking on FlyerTalk in the first place.