They are both very good at their job, but John Carmack has shown supreme capacity and skill that still is unmatched IMO. His superior skills has been proven time after time in ID's games, and the Doom3 just underline that fact. I don't know anything about Tim Sweeny's work, how important he is to Epics games, but as the Unreal Engines are without any doubt are great ones, there has always been a superior engine out - Carmacks.
In any case, in glad that they are both in the industri and I'm delighted for their work and products
PS: All this could
also change when Epic release Unreal 3? But I guess that Carmack and Co. will have something new ready for us at that time. I just don't see why we should talk so competative about these two fellos, I just see them as great people who have attribute that has contributed greatly to the industri and all the gamers