MESS is a greater emulator for older machines that do not have dedicated emulation software for them. I recall a time when it was the only reliable way to run Vectrex games on a WinNT/2000 system.
I met Vincent at a conference last year and bumped into him again a few weeks ago. If anyone is interested, he's currently working on the EU-funded KEEP project. See http://www.keep-project.eu/ezpub2/index.php
for more info.