djb is in no way the best programmer of the world, but he is a very smart programmer, and probably an even better mathematician. And now, my arguments about why he is not the best programmer.
1) djb software is not the most elegant software around at all. Actually trying to write high performance and bug free software his style is the most procedural possible, with very little abstractions layers.
2) his software is well known to be uneasy to configure. There are qmail hackers around. When there are <name of a unix deamon>-hackers around it's a bad sign about the quality of the interface between the program and the rest of the system and the system administrator itself.
3) Djb played no role at all in the programming languages world. AFAIK he never suggested some new idea for programming languages or new directions that are now considered important. You can't be the best without being influential in the field.
4) Djb newer wrote big systems that were crucial for the programming world. Qmail and djbdns can disappear tomorrow and everything will be up and running anyway. GCC or the Linux Kernel are a different matter.
I can continue, but I think 1+2+3+4 are already enough to deny the argument aaronsw is trying to push in the article.