Piccolo is one of the most intelligent fighters and characters in Dragon Ball. It's what's continued to make him at least somewhat relevant in Super, despite the huge power creep of the Saiyans. Even Beerus and Whis recognize his battle prowess, saying nothing when he was Gohan's first choice for the tournament of power.
He's one of the few Z fighters that hasn't succumb to his ego regularly, unlike Vegeta or Goku. There still have been a few decisions that were more than a little questionable. They just end up getting outweighed by his moments of brilliance.
10 Wrong: Increasing His Size Vs Goku
His decision to grow larger allowed Goku to save Kami from inside Piccolo after he ate the bottle Kami was sealed in. He grew so large that Goku was able to fly inside of him, a mistake that never should have been made in the first place. While size can give you a greater strength advantage, it makes you a bigger target as well. It's never made sense to use in a 1 on 1 fight, better suited for a large scale war, as the Saiyans used their giant ape form. It's a form made for destruction, not single combat.
9 Smarter: Reflecting The Evil Containment Field
This was a major moment towards the end of the original series. Kami, pretending to be a human named Hero, tried to use the Evil Containment Field on Piccolo Jr. He was hoping it would seal aways his evil for good. Little did he know, Piccolo had learned to counter the move, reflecting it at Kami. It was the perfect way to both handle a fight between them as well as show how much more of a threat Piccolo was compared to his father.
8 Wrong: Trying To Fight Frieza Himself
To say Piccolo was confident when he arrived on Namek would be an understatement. He thought he could take Frieza even before his fusion with Nail, confidence only growing afterward.
He felt himself an avenger to his people, the man who was destined to bring the evil despot down for everything he'd done to the planet. At first, he's correct, but soon, it's revealed what a falsehood that was as Frieza changes into his third form and easily overpowers Piccolo.
7 Smarter: Making Goku's Arms And Legs Useless
The strategy may not have worked out perfectly, Goku still winning the fight, but it doesn't change that it was sound decision making by Piccolo. He kept showing that he'd learned from the mistakes of his father, and he wasn't going to be taken down in the same way. He eliminated the use of Goku's appendages via his Mouth Energy Wave, crippling the Sayian. If he were dealing with anyone else, that would have effectively ended the fight, but Goku never gives up.
6 Wrong: Letting Himself Get Suckered Into Taking A Driver's Test
This episode is proof that sometimes, filler episodes can be amazing. Seeing Goku and Piccolo get suckered into taking a driving test because of Chi-Chi was amazing, from Piccolo wearing normal clothes to the two of them trying to race each other in their cars. For as funny as it was, it was still a dumb decision by Piccolo when he has no reason to be scared of Chi-Chi. It isn't like she's his wife and he has no real use for a car considering he can fly.
5 Smarter: Joining Forces With Goku
At the moment, Piccolo's only goal in life was still to avenge his father and defeat Goku. The arrival of Raditz put a new foil into that plan, a foe that was too strong for them to ever handle on their own.
Knowing that and acting on it are two different things, however. Ego plays such a huge role in Dragon Ball that you never know when it's going to crop up. He smartly put aside his difference to eliminate the bigger threat, even achieving his goal in the end by killing Goku.
4 Wrong: Charging Dabura
On the surface, rushing an opponent without having a gauge for their abilities is never a smart thing and something a strategist like Piccolo would rarely do. It's made even worse when you consider Piccolo literally saw Dabura spit on Krillin. Why then would you just bum rush an opponent that clearly uses it as part of his fighting style? It's a moment in the show that feels entirely out of character for the Namek, there just to prop up Dabura for no real reason since he's far from a threat in the arc.
3 Smarter: Ordering Gohan To Watch Chiaotzu's Sacrifice
This scene still holds up today, showing that even the Dragon Balls can't suck the emotion out of a scene. Chiaotzu's death did a great job of both building up the foes and giving stakes to events. It was also a moment that Piccolo smartly used to make Gohan understand why it was so important to grow stronger. Gohan owed it to his friends and the whole world to reach his full potential, that he always had to give it everything he had.
2 Wrong: His Resistance To Kami
Piccolo and Kami's relationship has always been strained, and that's putting it lightly. They constantly argue like a pair of siblings, Piccolo always seeing himself above Kami. He views him as his weaker half, someone who is only there so the Dragon Balls continue to exist. This causes a bit of a problem during the Cell saga when pride nearly gets in the way of them fusing. Thankfully, Kami manages to be the bigger man, having realized how necessary the fusion was.
1 Smarter: Giving Goku Time To Finish The Spirit Bomb
Far too often, characters will just standoff on the sidelines and watch characters fight in Dragon Ball. Usually, they are there to either commentate or offer that same shocked expression of fear over a villain's power levels. It's what made it so nice when Piccolo took the remaining energy of Gohan and Krillin, launching into battle with Frieza just long enough for Goku to finish completing his spirit bomb. It may not have been successful, but that doesn't change what a smart move it was.