I've been 3D printing for about 10 years. Played with scores of printers, filaments, build plates, etc. The best combo I have found is glass buildplate, Buildtak and a light coat of Elmer's Glue stick.
Put the finished printed into the fridge for about 30 minutes. Prints will pop off easily with a putty knife and gentle tab from a small hammer and doesn't make a ness.
Works every time! And I never use brim/raft/skirt for build plate adhesion.
Works for PLA & ABS and their variants.
I am planning the try a flex build plate soon. My main concern is the 'flatness' of the flex plate over time.