Also, most source ports have goodies for compatibility with modern hardware. EDuke32 is a jack-of-all-trades port, it does everything great except for multiplayer. DXX-Rebirth is a nice recreation of Descent in modern PCs.
The only situation I can recall where a DOS executable is preferred over a source port is if you're speedrunning Doom, because Compet-N doesn't accept records achieved using most source ports.
Also, I feel somewhat guilty playing DOS over a source port. I mean, in the case of EDuke32, it's been 10 years of hard work. Preferring the "worse" version instead of a source port feels wrong to me.
