If lounge access is your top priority, then DL would NOT be the airline to credit to if you ever plan to fly regular economy because DL dropped SkyClub access for DL Gold/Platinum/Diamonds (SkyTeam Elite Plus who earned SkyTeam Elite Plus through their DL status) if flying in Economy (Main Cabin or Comfort Plus). However, if you earn SkyTeam Elite Plus status through another program (Virgin Atlantic, AF/KLM, etc.) then you would be able to access the DL SkyClubs at JFK even if flying in Economy. DL will grant SkyClub access to Gold/Platinum/Diamond Medallions if flying in Premium Select/Premium Economy (and Delta One but D1 would grant access to the SkyClub and D1 Lounge anyway).