Both of those space vehicles are meant to carry out different tasks. How are materials selected for both of them such that it benefits their task? And is size a debatable factor while building these space vehicles? Is there an ideal preferred size for building a satellite and a space probe?
The big difference is in weight. Satellites in Earth orbit can be much heavier than deep space probes, simply because it takes a lot of energy to launch something into an Earth-escape trajectory. Satellites are often in the region of 8 tons, while deep space probes are rarely above 1 ton.
The materials are mostly the same. Aluminium for the structure, the usual semiconductors for the electronics and power system etc. The materials used for the payload (instruments) depends on the instruments. Common materials are used when possible, but in extreme cases unusual materials can be used: one example is the mirrors for the James Webb infrared telescope: these are made in Beryllium (because it is light and stiff, so a large mirror can be used within the weight budget).
Plutonium-238 is somewhat common in deep space probes (eps. missions to the outer solar system) and very uncommon on Earth-orbiting satellites. Pu-238 is used as the energy source in radiothermal generators (RTG), which are used for missions where solar panels can't be used (because they'd make the probe too heavy to be launched).
Materials are selected based on the purpose of an instrument, and the environment it has to operate in. The list of requirements is long, here are a few examples.
- telescopes use materials that don't expand or contract when the temperature changes, to reduce distortion
- a space probe that has to operate in an environment with a lot of radiation (e.g. Jupiter orbit) needs radiation shielding
- infrared telescopes have to be cooled, so they have to use materials that work well at low temperatures
Because a spacecraft can't generally be repaired after launch, there is a tendency to be conservative. Only proven materials are used.