As a former army officer well versed in NBCW (Nuclear, Chemical and Biological Warfare) my first question is "what will be left to survive for?" The destruction of the infrastructure of our civilization will reduce the remnants of humanity to a new dark ages. At my age I would not want to face that.
As an army officer (in intelligence,) you wouldn't want to face the
civilian future of that event. But, Cheyenne and other places wi be full of people waiting to resurface and restart once the dust settles.
They are likely doing that now.
As far as surviving a nuclear or bio attack, either is horrible. But, I would personally rather survive a nuclear situation than a biological one.
Maybe it is because I am a physicist and not a biologist I find dealing with nuclear radiation easier than a bio attack. I know most all nuclear bombs fissile into Iodine-133, which has a half life of 8-9 days. So, stay out of, and away from fallout for two weeks.
You can also make stage filters even for irradiated water! The one I usually go for is a seven stage filtration system that uses everything from sand to a cotton shirt. It works.
Also, as you mentioned, because most attacking countries will want to salvage infrastructure, the chances of multiple high yield bombs (>10) is absolute unlikely - even for psychopaths.
If a 20MT nuke was detonated over a major city, it would have a radius of obliteration of about five miles. Ten miles out, you get severe radiation, severe pressure damage, and severe heat damage. 20 miles out, and you are starting to get in the clear - moderate to light radiation, light to moderate heat and pressure damage.
Likely, the yield that will be used in conflagrations would be bombs under 1MT. Multiple small yield nukes tactically detonated is more likely tHan a city destroyer detonation like a Tsar Bomb.
(This is not to mention there are more energetic, destructive WMDs that yield little to no radiation.)
The nuke option is for fear, and to cause total faithlessness. It is, now, more of a psychological weapon.
Biological weapons are vast, and diverse. It isn't as straight forward as nuclear physics; we know the certain fissible elements that can produce nukes, and their daughter particles and decay. There are ways to decontamination yourself, and protect yourself from nuclear danger.
Biological attacks are actually much more serious than nuclear. And, they are unpredictable (perhaps, unless you are a biologist or study biology extensively.) Even then, you will likely need resources, technology and such to even begin working on remedies.
There are even supplements you can take to chelate radionuclei from your body. But, biological attacks are another beast altogether.
Also, chemical, radiological (different from nuclear,) and epidemilogical (different from biological) dangers are also extremely dangerous. I would pit nuclear last in terms of "danger/scariness."
