A collague of mine wants to switch from AA to SkyTeam, now I did switch to CO a while ago but dont know if it might be better to advise him towards DL or NW !?

Is there any downside with either one of these programms ?

I only flew on CO as long as I have my status but in general, how do the Alliance Partner treat you in terms of upgrades etc ?

Would it make sense for him to match to DL (flying LAX-JFK) when he is looking for preferential treatment on some NW overseas trips

Cheers,