If asked their favorite Dragon Ball Z character, most people would say Goku, Gohan, or Vegeta, but I am not most people. My favorite character, in contrast, is Piccolo. Piccolo is a Namek who was originally created, by the Evil King Piccolo, to destroy Goku. However, after training Goku's son, Gohan, and fighting along side him for a long time, Piccolo begins to soften up and work with Goku as an admirable and indespensable member of the Z Fighters. There are many reasons why Piccolo is my favorite character, as unorthodox as it may be.
For one thing, out of all the Z Fighters, Piccolo is the most intelligent. He shows this fact time and time again throughout the series. Piccolo fights not only with brute strength, but also with his mind. Goku and Vegeta may have the aptitude of grade school children, and Gohan, though quite intelligent, usually fights more with instinct. Piccolo will usually be the one who thinks about the moves he makes before he makes them. He always finds a way to think clearly and always executes his moves with his own abilities and the abilities of his opponents in mind. Sometimes, he has the tendency to miscalculate, but as the series has shown, not very often.
Another reason I like Piccolo is for his versatile skill set. There are so many attacks he can use in a fight. He has as much versatility in his list of attacks Goku and Vegeta do. He has the ability to stretch his arms to unknown lengths, shape shift, fire lasers from his eyes (which he uses less frequently), can read minds, regenerate himself, and telepathically communicate with others. His attacks include the Destructive Wave, Special Beam Cannon, Light Grenade, Masenko, Scatter Shot, and Hellzone Grenade (my personal favorite, where he suspends many chi blasts into the air, surrounds the opponent with them, and explodes them at the target all at once). There is no character, in my opinion, that can be as much of an asset in a fight than Piccolo, even if he is not the one fighting.
With his mind sharp, his versatility mind-boggling, and his strength herculean in many ways, Piccolo is, in my opinion, the epitome of the ideal Z Fighter. He has the intelligence to match his strength, and an endless amount of possibilities for attack combinations. Could this be enough to make him the best of them all? No. The one thing that my favorite character lacked was a pure heart, filled with determination. This pure heart was the one possessed by Goku, and due to the fact that Piccolo's heart was not always in it, Goku surpassed him. Goku also received more special training, while Piccolo played the role of the trainer, training Gohan, and later Goten and Trunks. I hope this satisfies any readers wondering why I would not pick Goku or Vegeta, but rather, Piccolo as my favorite character in Dragon Ball Z.

Comments
My favourite was always Trunks. Specifically, the older trunks that came from the future to stop the green coloured dude.
Mostly because of his awesome hair, and the fact that he was the only one of those people to carry around a sword.
I mean swords and freaking awesome. Who needs giant balls of magic when you can just cut and chop the enemy into a million pieces.
Other than him, I suppose Goku was my favourite. Although, for some reason, I despised Piccolo.