If I can only choose one, it would be the spoon, because it will be easier to get that last little bit out.
And that is assuming those are my only choices for emptying the tub.
After enjoying a long soak while playing with the cup, spoon, & a floating bucket, I would pull the plug to let the water out, then rinse the tub round like a good boy Lmao :-)
i would unplug the plug
as mariusthered said I'd pull the plug