What the most important body part? ? ?

I reckon the back is the most important body part. As the back protects your spine. It also has the most potential for growth. The lower back is a crucial component of core stabilizing. The most unfortunate thing about your back is that you can never see it. which almost defeats the purpose of sculpturing your body as you cant witness the results of your hard work.

However the most enjoyable body part, and the one that does the most for self asteem (ego) is biceps.

The biceps being such a small muscle means you can work them really hard, and have them recover very quickly. when the biceps get the pump during a session its more stimulating and looks more impressive than any other body part when pumped.

In conclusion, I believe to have the most enjoyable and beneficial session is a combination of biceps and back, working the biggest muscle first because that will require more of your energy than biceps will, and will serve as a good warm up when commencing biceps training.

Strangely enough biceps are probably the least useful muscle in terms of what they contribute to the body but the most fun to workout, but as long as you feel good while working out that is the main thing.