If this is for archival use, I'll add another vote for LAME. It's the best MP3 encoder on the net, period. It's actually not an MP3 encoder (that's what the acronym LAME stands for, "Lame Ain't an Mp3 Encoder), because the developers have basically rebuilt the dang thing. There are many brilliant people working on LAME, and it gets significantly better with every release.
However, I really like the way
MPC sounds, so I suggest you have a trial of LAME vs. MPC. If you have a portable MP3 player for example, you'll want to stick with LAME. If you want the absolute best sound quality out of your files for their bitrates, you'll want to play with MPC. If you don't have the ears and/or equipment to hear >18KHz sound, MPC at 160Kbps cannot be beaten. If you can hear >18KHz, the other sound profiles which result in 190Kbps and 220Kbps for MPC will suit you best.