I've been using LameDropXPd for years. It's free and very simple, yet powerful. It places a "drop" icon on your screen where you drop the files to be converted & it does the conversion. You can right click the icon before conversion to set the particulars such as quality of the output and where you want the files to go. It uses the excellent LAME encoder for the best sounding tracks.
I also use the excellent FLACdrop too, which works the same way except it will encode wav files if you drop them onto it & will convert FLAC to wav if you drop FLAC files on to it, so it goes in both directions. I always convert a copy of my FLAC files wen I'm editing them because they lose tag info as a wav file. Then when I convert back to FLAC, I just open them up with MP3Tag along with the original FLAC & I can copy all of the tag info without typing everything.
So why did I buy Switch Plus? Because I can Normalize in bulk at high speed while converting! This makes all of my files have the same volume. I like to set it at around 97% so that I know I won't have any clipping. I had a problem with clipping at 100%, but never at 97% with another program I used, so I just continue to use that as my setting. The other program required me to do each file separately and that is very time consuming. If you ever want to listen to your songs on random and they all have different volumes, you know how vital normalizing can be!