Though if you are elite on the Skyteam, the upgrade to F is automatic (based on availability of course), not the case on AA or UA.
For us being non-elite but having miles, the value of miles would be much more important, naturally.
Of course, in general it also depends a lot where one lives - which airline(s) hub is the closest major airport determine which airline you fly the most. Or, in our case, where we want to go in the world also dictate which airline's FF we want to accumulate miles the most.
There is a little-known secret: AS miles can be earned on Oneworld partners as well as Skyteam partners - and can be redeemed the same way with much more availability. I believe it is because there are a lot less AS members to fight for award seats on high-demand routes. A friend recently redeemed his AS miles for 3 business seats to Sydney on Qantas - he could not even get 1 business seat using AA program, and he could do it with AS miles, all 3 seats on the dates he wanted, with 5K miles less per seat!