Which unfinished fight would you most want to see the end of

[Piccolo Daimao]

There would be reasons for him not using it. It was a last-ditch technique, which is why he only used it against Cell when he was trying to absorb the Androids. There's the chance that #17 could dodge the attack, or the chance that it may not destroy him, which would only end up exhausting Piccolo's already waning energy and make him live bait to #17, who has infinite energy and an energy shield (which he proved was capable to guarding against attacks with the Hellzone Grenade). Yes, it was the same case with Cell (the chance that it may not destroy him, I mean, not the infinite energy), but that was when it was all or nothing, and he only had one objective in mind: killing Cell and stopping him for absorbing #17 & #18. Piccolo still had somewhat of a chance of defeating #17, since he was even with him.

If Piccolo was about to lose, he'd do whatever it takes to prevent it. An imminent loss is worthy of using a last-ditch technique, a desperation move, or whatever else it's to be called. Yeah, #17 could've dodged it. But then again, Cell could've dodged it, as well. Yeah, it may not have killed #17...but it may not have killed Cell, either (which was already touched upon, obviously). You can say that for practically any ki blast used in the series. I'm pretty sure #17's "Look at me, I shielded myself from multiple generic ki blasts with mah barrier" wouldn't serve to dissuade Piccolo from trying out his strongest attack. If push came to shove.

Yeah, you're right. If #17 had pushed Piccolo enough, he would've eventually been forced to pull out all the stops to kill him.