Which object exerts more gravitational force, object a with a mass of 25 grams and a density of 2 g/cm3 or object b with a mass of 55 grams and a density of 0.5 g/cm3?

It all depends how far you are from either object.

Whatever your distance is from the 25gm object, the 55gm object
will attract you more strongly if you're less than 1.56 times that same
distance from it.

As long as you stay at least 1.56 times as far from the 55gm object
as you are from the 25gm object, the gravitational attraction toward
the more massive one will be the same or less than the attraction
toward the less massive one.

It's entirely up to you.  You can choose which one you want to be
attracted to more strongly, and then you can make it so.

Like if you go close enough to the moon, then the moon will pull
more strongly on you, even though the Earth has more than 80 times
as much mass.

And if you stay close enough to the Earth, then it pulls on you
more strongly than the sun does, even though the sun has
333,000 times as much mass as the Earth has !