I guess I'll be the first to break from the majority.
The WTC center holds too many important facilities, organizations and headquarters in the same place. As I understand it, the NYPD headquarters were located in the WTC, which compounded today's situation. It seems like a case of putting all of our collective eggs in one basket. Today, large portions of New York's disaster management and the nation's financial infrastructure were crippled because of this. The WTC has already been the target of two terrorist attacks, and rebuilding it similar to before seems like asking for more trouble.
I'd prefer that a monument be constructed there, while the various parties who were once housed at the center be distributed across the city to prevent another such crippling attack.
I realize that if we didn't rebuild, it would seem like we are giving in to the terrorists. But I think it's more important that we rebuild ourselves defensively to make it harder for another tragedy like today to occur.