What are the "best transcodes" to use?

[roydbt]

I am planning to pre-transcode a movie I have from 2160p to both 1080p and 720p so that my RasPi doesn't have to do the work every time I want to stream the film. I have (almost) never used ffmpeg and I don't know a thing about the different codecs there are. What should be my best options to transcode the movie to reserve the quality of the original file?