Would Nuclear War or Biological War be worse and why?

Nuclear, because they are more indiscriminate. Biological warfare is directed at people. Nuclear explosions cause immediate widespread destruction, and nuclear fallout poisons the soil and the water for thousands of years.

bio weapons are militarily useless

thats why no major country has them or uses them

Nuclear. The fallout will kill more than the initial blast. And the fallout will be carried across the country and around the world. This will irreparably damage the ground, animals, and the air we breathe.

All the weaponized biological agents that the US and the former USSR have, have very short life spans and are not contagious. That's why one can die from these agents within minutes of exposure. To make it contagious means you would have to drastically reduce the lethality so it can be transferred between people. Reduce the leathality and that means a majority of the people exposed will not die from it.

I would argue Biological. The reason being is that, and while it does depend on the specific agent but i we're talking in general, a biological attack will spread but a nuclear attack will not. Nuke say Denver and whilst radiation will spread in the local area it will remain local. Unleash a biological agent in Denver and if active measures are not taken it will not remain local. Just look at how quickly Covid-19 has spread in the US alone. At one point there was only one person with it and now? This is the problem with biological weapons, they can be very difficult to control and places the user at far greater risk of being hurt by their own weapon compared to almsot any other.