I feel like this is a really good match up and I really really wanna say Goku but I just feel like I can't.
Its difficult to say. We don't know how strong both the Androids are, they could be way way weaker than Frieza or much stronger. We also don't know how much energy Dr.Gero absorbed from SSJ Vegeta's Big Bang Attack and Piccolo's own energy. When Piccolo decided to fight Dr.Gero Vegeta said (Anime) that he didn't care if Piccolo where to die but he did care if Dr.Gero manages to absorb more energy to make himself stronger, does that mean if Dr.Gero was at his maximum that he might pose a problem for Vegeta? Dr.Gero also said (Anime) in order to achive success (debatable) he needs to be at maximum capacity, Dr.Gero apperently wasn't at his best. But Dr.Gero could have ofcourse be completly wrong because he also though he could take on Piccolo but, Piccolo turned GOD MODE ON and Layeth the Smackdown on Dr.Gero.
It was a stomp. Dr.Gero was facing Piccolo and Piccolo rushed him and he could't follow him. He then tried to counter and Piccolo was still WAY to fast for him. He then CHOPPED his arm clean off. Dispite not knowing how strong both are Piccolo might have an advantage. Piccolo trained with Goku AFTER he came back so technically should't Piccolo have an advantage in fighting because he knows how Goku fights and knows about his IT? remember this is Piccolo after he fused with Nail so Piccolo might suprise Goku with some new moves.
EDIT: There is something worth mentioning. When Android 18 broke Vegeta's arm and Trunks rushed in Android 17 hit Trunks with a suprise attack. Piccolo then rushed in and recieved a kick to the head. Trunks got up but was held back by the foot by Android 18 who trew Trunks into Vegeta. Piccolo surprisingly stood up and was ready for more, ofcourse he got kicked back again but its worth noting that like Trunks after he got hit he stood up and was battle ready. Trunks when he first met Goku should't be THAT much weaker than Goku right? Maybe this is more of a close battle than i thought.
I don't know if this is Vegeta's ego playing but dispite Vegeta crushing Android 19 that damn robot still got up even after Vegeta delivered some brutal hits, Vegeta needed to put some effort into escaping Android 19's hold. What i find strange is Piccolo who fought an amped up Dr.Gero he easily chopped his arm of like it was nothing. Piccolo made Dr.Gero look like a cheap Toys"R"Us robot you buy in the bin, Dr.Gero could't even follow him let alone hit him.
Piccolo should know about Goku's IT and some of his technique/moves since he trained with him for 3 years. This Goku however is Pre Android so he doesn't know all of Piccolo's moves he's learned during his stay on King Kai Planet and fusing with Nail so Piccolo might suprise Goku with a few new tricks.
Piccolo can die too. Nappa didn't destroy his head, still killed him. Freeza beaten Piccolo too. Goku KO'd him on the tournament.
There are some hint/reference in the series that the super saiyans is above Piccolo.(but these are long sentences so I don't write it :P) And the virus causing that Goku was getting weaker. I think a healthy Goku would beat Piccolo.
I know, it's true to all dbz character. The lower their ki, the lower their durability. Regenerating suck off Piccolo ki. And when they fight. My point was he not immortal against Goku, Goku have chance. But I admit I was wrong. That hint what I thought is said when Trunks, Piccolo, Tien and Krillin was talking, but I forgot that they said the current Goku, not the pre-3 years Goku. :P
So I agreed with the others, they are around the on same strength, but Piccolo know how Goku fight. Goku only chance if they charge against each other a kamehameha and makankosanpo, and when piccolo shot, Goku use IT. (he couldn't dogde that, and he wouldn't expecting that because they training, fighting on that 3 years not learning tactics)