Anyways from Gary I liked Assassinate Hitler and Schabbs 2000 very much (along with Episode Four/Countdown to Disaster but those weren't released until late 2001/2002 when the source code was clearly out already). And from Barry Christian, I'm not a big fan of a lot of his earlier works (all he way up to Six Depths of Terrorism, to be honest, though that and Domination are okay), but I remember immensely enjoying Armageddon and The Road to Neushwanstein. So in the timeframe of focus it happens to be two major games from each author.
On the topic of Barry's works, I didn't like the occasional hidden keys and am tempted to knock a little off because there are no skill settings as far as I can tell, but one strength to both Armageddon and TRTN is that they are well-structured mods and have very memorable endings. For Gary, I don't recall the endings being nearly as memorable, but the mapping itself is just as good IMO, there are skill settings, and I don't recall any mandatory items being hidden behind a pushwall.
So in the end, I can greatly appreciate both authors' works and I think all four games I'm mentioning are excellent mods, but honestly I can't say for sure which one I like better as they both have a few unique strengths as well as slight weaknesses.
As thus, that being said, who do you prefer (or do you have a general tie between the two as well)?