It would help to know where you would tend to fly on SkyTeam. Meantime ...
SkyTeam lounge access is available to SkyTeam Elite Plus members on an international itinerary so it isn't much help say to have AF Frequence Plus Rouge if you fly DL all the time.
Elite Plus in Skyteam comes at 100k qualification miles on DL and 75k qualification miles on NW and CO while if you have a north american address AF F+ Rouge is only 40k qualification miles.
Priority boarding is recognised across the various SkyTeam FF programs.