Curious. GaN or SiC?

GaN or SiC That depends on what you want to do.
SiC can be high voltage while GaN is lower. I only know of one 900V GaN, most are 600V and down. Some SiC are up to 3000 volts.
GaN is faster. It is a little hard to make work because of the speed.
What are you working on? I have done SiC and am fighting with several GaN designs right now. When you have questions just ask. There are several people that work GaN who might be able to help.