Bismuth or Indium solder - how do they compare?
They are very expensive. Some of them are outright forbidden (e.g. all Cadmium based alloys). These special alloys are made for special needs: Low temperature soldering (e.g. if you have a 100°C thermal fuse, you cannot solder it with normal solder), low EMF (e.g. if you want to measure voltages with &lt;100µV of accuracy), etc pp. Unless you are doing very special stuff you will not need them.