What's the difference between the dithers for recording?

I noticed in the preferences menu for Audacity that there are real time dithers and high quality dithers. I picked Shaped cause I think it sounded better than the others (long time ago since I changed that → I have no idea why I did it but I love high quality audio so that’s probably why lol).

Either way, what’s the best way I can get good quality mp3s on Audacity? (I already use 320 kbps)

“Dither” applies a tiny weeny teeny bit of noise to the audio when it is “down-sampled” from a high bit depth to a lower bit depth (for example from 32 bit to 16 bit). This is to smooth out the slight jumps in volume that will occur when the signal approaches silence. There are different ways that noise can be added, but in the case of “shaped”, so as to be as unobtrusive as possible, this noise is “shaped” so that there is less noise in the parts of the audio frequency spectrum where low level hearing is most sensitive. The different types of dither are just different ways of adding noise. Any of the dither types will work and there is very little noticeable difference - the default works well.

Dithering takes a little bit more effort for your computer than playing without dither, so for real-time play the default is to not use dither, but when any data is actually written/changed (for example when Exporting a file) the default setting is to apply “High-quality dither”.

320kbps CBR is the highest quality format for MP3. For higher quality, you could use Ogg at the highest quality, or FLAC (only around 50% compression, but lossless), or uncompressed audio.

Of course, the quality of your recording is of paramount importance.

As always, you’re the man, Steve. Thanks for helping me out with dithers.

So, just I have Default Sample Format to 32 Bit Float, both the real tie sample rate converter and high quality sample rate converter to high quality sync, real time dither to none, and high quality dither to shaped. Is this good?

The “Real-Time Conversion” can be set to “Fast sinc / Dither none”
This will make no difference to the finished product, but will give marginally better performance.
Other than that your settings are fine.