I just looked through my operator list and found I had the following operators with max skill level with Operators marked with New are ones I got to SL7 today:
Amiya
Ansel
Beagle
Cardigan (New)
Cuora
Exusiai
Fang
Gummy
Hibiscus
Ifrit
Jessica (New)
Kroos (New)
Lappland
Lava
Liskarm (New)
Melantha
Mousse
Nearl
Orchid (New)
Perfumer
Plume
Popukar
Skadi
Steward
Texas
Vanilla
Vigna
W (New)
I'm considering maxing out:
Adnachiel: SL5
Blaze SL4
Ceylon SL6
Gavial SL5
Grani SL3
Nightingale SL5
Podenco SL6
Shaw SL6
Silence SL5
Tomimi SL5
Any ideas of which operators I should do first?