I've had A LOT of really nice custom flippers:
RJ Martin Overkill/Modulator - super sharp, fast flippers, kinda harder detents; for the larger 3.5 blades they carried light and slim
McGinnis Severen/etc - Love his organic designs and his hole patterns keep them really light. for a non bearing flipper, Gerry makes the best action I've had
Ochs - big fan of his hammered style
Mosiers Creep/Spyro
Lambert Snap MGT
Begg Mini Glimpse, Bodega
Shirogorov - back when they were going for $600
several Hinderers.... etc. etc.
If you can get your hands on any of those, you'd probably be happy.
As far as production flippers - I like the Spyderco Southard
I ultimately moved away from flipper knives - I now prefer a thumb stud or disk. Go figure...
The ONLY flipper I wish I didn't part with was a Phil Bogi Proto Mini Cobra