Manu admin is a very popular admin mod, but is one of the worst. It's commands are just running off of the rcon commands (like all admin mods), but with no additional features. Also, It's unbelievably insecure, I've seen alot of servers running manu, and 90% of them have been hacked.
b3 is my personal favorite, It's secure (with tweaking), reliable, easy to use, and a fully functioning system that warns people automatically.
But, IceOps's cod4x is still very good, not only is it secure, it's made by the IceOps team.