ashampoo music studio is good for converting audio its not free but its on the sister site.

 

since then, Reaper's batch converter can utilize all the cpu cores, so it's hand down my go-to,
hours of audio take seconds to convert, even on 13 years old MacPro

 

if you use Process explorer from sysinternals you can see the process running and how many cores its using and you can change the priority of the process to make it faster or slower and you can pick which cores you want it to run on.

 

Yeah, I could see that. It's just to avoid the hassle of tryin' them because some companies omit this important data in their specs.

I'm more than well served with dbPowerAmp Converter. Hard to look back after you try it.
Although I'm sure last Reaper versions could give it a run for his money I'm used to it.

 

I'm covered by the last few mentioned here —Ashampoo and Reaper—but my go-to is Studio One's Batch Convertor.