I don't know if it's the best, especially if you're converting more than one
at a time, but Audacity can do it.

Many music players that come with Linux distros can do it and you can even
use VLC. Best? That means different things to different people. Some
commandline junkies would say one thing and GUI lovers say another. A KDE
user would prefer one application while a GNOME or Unity user another. There
is SoundConverter (GNOME) and SoundKonverter (KDE) for example. either will
install in Ubuntu and both are in the repositories. You did not look very
hard. :) Tip: You can search Software Centre or Synaptic for mp3 wav and it
will give you suggested software.

Commandline love:
linuxpoison.blogspot.com/.../...rt-wav-to-mp3.html

I did do that but the ones I got converted to pretty much everything BUT
mp3.

Audacity will do it fine and even can do some very advanced batch
processing too - took me a while to find it as they call it chains.

Look under [ File / Edit Chains ] to create your own conversion scheme
then go to [ File / Apply Chain ] to select a folder to convert and
the 'Chain' you wish to apply - puts all the processed files in a sub
folder called 'Cleaned'.

Yes it is a strange way of doing it, but it actually works very well
and I'm sure can be very powerful with a bit of investigation of the
command structure for chains.

I learned something today. I've only used Audacity for the simplest of
tasks. Thanks for that mini-tutorial.

Ditto with Audacity - it was when I had a huge folder of MP3's to
normalize and then re-save at a lower bitrate for an MP3 player that
the need to investigate batch processing arose. Pleasantly surprised
to find Audacity not only does this but so flexible too :-)

Definitely something I will keep in the back of my mind. I like using
Audacity.