I'd say they are around equals, with Piccolo possibly having the lead here. Whilst he was surprised by Freeza's chi, such is expected when the info he had was restricted to "Freeza is way stronger than Earth Vegeta". Sensing a power that is on par with his own and in the hundreds of thousands would warrant such. He still goes to the battle field with the mentality of saving the boys, as he said to Nail. So I don't think Freeza's powers far outstripped Piccolo's until he was about to finish his power up, which was when Nail pointed out Piccolo would have no chance.
Whilst you could say that Piccolo was cosiderably weaker but they'd manage a win in the end with a team work, I find that doubtful as Freeza seems skeptical at the belief of the Ginyu force being brought down by Vegeta, Gohan and Kuririn in a time he had his scouter, so I think they were suppressed to levels at least below Captain Ginyu and therefore Piccolo would consider that when sensing their chi.