You will get as many answers as there are POTN users and it obviously depends on the portrait application, so I don’t think there is a “best”.
GONZOGOLF is a smart guy, with logical good advice!
I am only one comment, but after numerous years of many product iterations, the ROGUE is my favorite - for its practical, very flexible solution for both on camera or off camera flash needs.
ROGUE FLASH BENDER:
It works as a creatively pliable/bendable bounce, snoot and grid(with a Rogue grid).
Also, I have found Neil Van Niekerk techniques and perspective useful:
Rogue Flash Bender sometimes combined with STOFEN Omni BOUNCER [a.k.a. your "simple one" & as PEARLALLICA commented and I too have found provides pleasant soft light], for pleasing results (inside or occasionally outside) by any criteria.
Others will praise other products, everyone has their own preference.
Pardon me for commenting on a basic point – Strategy: start with what portrait image you want to achieve and work backwards, as to what light behavior is needed and then what technique or product aid to achieve that image. You may want to rethink your view i.e. from on camera to off camera (even without an assistant).
Good luck on determining a solution that works for YOU and YOUR style.