To me nothing beats the original hardware for gaming, but lacking this hardware (or the space to set all of it up) an emulator is the next best thing.
There are also different levels of emulating. A console is preffered to a computer for emulating console games. The dreamcast is nice for playing ATARI 2600 games then the PC because it still uses a TV for output (pc's with tv output are not as good as far as I am concerned).
Has anybody ever played battlezone on an EMU that would come close to rivalling the feelling of looking through the viewfinder of the real machine? The only real way to play centipede is with the original roller ball. I guess if you never touched the originals then maybe an EMU is probably good enough.