What is the difference between suffix or and er?

Answer 1

The -er suffix is Germanic and the -or suffix is Latin. Generally speaking, if the the English word derives directly from a Latin agent noun, such as orator or professor, it retains the -or ending. Otherwise, our native -er suffix is used.

Answer 2

The suffix "or" typically indicates a person or thing that performs an action or holds a certain quality (e.g., actor, creator). On the other hand, the suffix "er" usually denotes a comparative form, such as bigger or faster.