I'm assuming this is Piccolo right before he fused with Nail?
It's probably a hard fight because of Tien, but Piccolo wins. 9/10 times. I'd say the 1 loss is Chiaotzu blowing up on him and Tien capitalizing on the damage.
Because Piccolo started out like >>>>>>>>>>>>>>>>>>>>>>>>>>>Tien & Friends, so no matter how much training the humans do, any equal training Piccolo does will always keep him magnitudes stronger than them.
Going with Piccolo.
When he first arrived on Namek(before fusing with Nail), Piccolo could sense 1st form Freeza's power, and still rushed that way to fight him:
http://i.imgur.com/qicRu4F.jpg
Piccolo didn't even get discouraged when he sensed Freeza's ki after he fully powered up:
http://i.imgur.com/hkOELRW.jpg
I don't think Piccolo would have been nearly as confident that he could help beat Freeza, if his PL weren't at least in the same ballpark. So it seems logical to assume he was somewhere around the 400-500k mark at the time(1st form Freeza=530k.)
This is important because at that point in the series, the other undead Z fighters likely weren't even close to that level. After all, Krillin, who has been confirmed as the most powerful Earthling multiple times, only had a PL of 75k during the Freeza saga(post-Guru-unlock), so yeah...
Anyway, the only one here who *might* be able to harm Piccolo is Tien, via Kikoho... But that's only if he'd learned to use the Shin Kikoho(ie. a mastered Kikoho) at that point in time... Because during the Saiyan saga, he definitely hadn't yet mastered it--as evident when Nappa tanked it.
