I teach my students and black belts that no one aspect of Taekwondo is more important than another.  Sparring is just as important as poomse, which is just as important as one-steps, which is just as important as terminology, etc.  It's like the peddles on a flower.  All are a part of the whole, with all being equally important

I'll try and keep this succinct, although I will be the first to admit that I tend to get a bit wordy at times...

Forms:  In my opinion, forms teach balance, targeted application of technique, simulated defense against multiple attackers, and, perhaps most importantly, self-discipline and concentration.  It works both sides of the brain, as the student that really attempts to make the performance of a particular form a work of art gets to push their creative centers as well as working the cognitive reasoning centers.

One-Steps:  In my opinion, one-steps teach instantaneous reaction.  At least, it forms the basis for much self-defense.  I am a proponent of simplicity in one-steps.  I have a hard time seeing the validity of the one-step where you block, and do a 10 move counter that culminates in a jump 360 kick.  I try to emphasize to my students that the most important part of self-defense is being able to thwart the attack sufficiently for you to escape, not hold the bad guys down until the cops arrive.  Block, counter, and run like crazy. 

Terminology:  I think terminology is important for a couple of reasons.  First, it is a connection to the Korean tradition of Taekwondo.  Granted, my pronunciation is probably a bit weird to somebody else...after all, I grew up in North Dakota, therefore everybody else in the world has an accent . . .and we don't, right?  The words we use may be bit outdated, or referenced slightly differently, but I think the idea of a traditional connection is valid.

If I call a command "Chimbee", students don't approach it with preconceived notions based on the language.  Also, by the time students get to Black Belt, they often think of the commands in English and Korean.  By using Korean, many schools can get together and practice, and they don't have to take the time to translate all of the commands; they simply know the terms and execute.  Again, I think this helps their overall mental development, concentration and memorization skills.

As I said previously, I think each and every aspect of Taekwondo has something to teach the student, and that no one part is superior or more important than another, but all are necessary to create the whole person/whole martial artist.

I'm not saying my way is the only way, I'm just saying that after teaching for 16+ years, I found that if I can balance the whole, rather than focus on one particular aspect, I am able to teach life skills to the student better.  And that, I think, is why I teach Taekwondo.  I'm not teaching how to kick and punch and yell so much as I have an obligation (or duty per se) to teach my students, both young and old, how to live a better life.  Taekwondo is just the vehicle that is used to accomplish this.