The uncertainties are of a different order for geothermal as it is a much more immature technology.
That assumes that you are talking about using it for really substantial power generation, which means hot dry rock.

A number of problems have been encountered, notably getting just the right amount of fractioning in the rock to allow the water to flow through to the well which extracts it, and that problem will be different for every field.

At present it also costs a fortune - that may change, but we are talking about uncertainties.

You also can't build a geothermal plant just anywhere, and practically speaking the areas where you can hope to build them are relatively limited.

You can say the same thing for Nuclear energy. Some of the questions might be who is going to finance them and do you want one in your backyard.

I'd like one under my backyard (say, 500 feet or so down) because then I'd have a cheap source of low-grade heat to keep my house heated in winter and perhaps cooled in summer with an absorption chiller.

As for what kind, I think the USA could start with roughly 100 GW of molten fluoride reactors operating as thorium breeders.  The initial fuel loads could be obtained from the plutonium in spent PWR fuel, eliminating it permanently.  Small, standard-sized reactors could be cranked out in factories in pieces small enough to be moved through tunnels and assembled underground, where they would be isolated from the environment (and terrorist-proof) but still very close to customers for waste heat.

Once you have supplied the local need for electricity, heating fuel and low-grade industrial process heat without a gram of fossil fuel, the impact of shrinking supplies becomes much more remote.