My personal opinion....
I prefer the Taegeuk forms, mostly
because of their simplicity which I believe is a better tool for creating quick, useful self defense reflexes. Complex forms are fine for Black Belts, and most of the people who question these kinds of things
are Black Belts who want more out of their forms. Most color belts have enough challenge to learn
one simple form per rank, and that's all they really need. I used to teach multiple forms because of attachment to past training, or my own preference for complex forms, but I find it does more harm than good.
My personal experience....
As a color belt, and beginner Instructor, I learned all of General Choi's Chang-Hon forms up to 6th Dan form when I was in the ATA in the 1970s (I was taught a few forms beyond my rank). In the '80s I learned all 8 of the Palgwe forms from a Jidokwan Korean Instructor just in time to switch to the Taegeuk. We taught both for a while but then dropped the Palgwe. I have had my fill of learning new forms, and switching back and forth. I find that any form done with excellence will score high at most tournaments (from my perspective as both a competitor and a judge).
My biggest concern is teaching forms that I hope will be in use five or ten years from now (so I won't have to switch again!), and that the practice of those forms addresses the issue of building better reflexes for self defense rather than if they seem challenging, complex, or entertaining enough. The same holds true for one-step sparring. More and more Black Belts want to make them complex and advanced, but for color belts, the simple, basic techniques works best in preparing reflex, and reality for self defense.
Just my thoughts on it!
CM D. J. Eisenhart