I use this. I "update" the encoder used in this software by replacing its DLLs with the one from the latest opus tools (this is the latest at the moment of writing)
Be sure to always select 48 khz sampling and VBR when encoding to OPUS
128 kbps should be transparent for most people, if you think you have excellent audio equipment and ears go with 160 kbps
Also, sometimes when you launch the program it gives you an error, just close it and try again