>>‘All Nukes’ is not the best policy<<
Yes it is
>> Yes it is <<
It depends on what you want to do.
For intelligence gathering in hostile environment a smaller sub with less crew might be better. A smaller submarine can get much closer to the shore.
Just compare a Virginia-class with a Type 214.
Crew: 135 / 27
Cost: $3b / $0.5b
Torpedoes: 26 (4)/ 13 (8)*
VLS: 12 / n.u.**
Endurance: unlimited (food supply) / 84 days
*: Type 212 (tubes)
**: not used but Vertical Multi Purpose Lock (VMPL) available, just like the ones on Block III Virginias.
Nuclear powered subs are faster but also much louder. Even a US nuclear submarine can’t be at two places at once.