Custom bike to offer smoothest possible ride on bad roads
Based on your requirements I would say full suspension fat bike
A few manufactures make them   

 

That bike is $6500 retail but you did not state a budget 

Not worth switching out tires as they are expensive but when you wear them out go with more street (will less knobby) tires   

If you are on a budget I think I would go with lower end fat bike before a full suspension.  But I am not saying full suspension would be wrong.  

I know I usually post a Salsa if I post a bike but I am not associated with Salsa.  I own 2 and it is a brand I am familiar with.