I know that there are several places where GuiXT scripts can be located:
Local computer
Central File Server
SAP Web Repository
HTTP Server
FTP Server
I also know that I can give each user the same guixt.ini file that points to a central guixt.ini.
But which choice would you recommend for 700+ users?

The most popular solution for larger user numbers is the Web Repository, combined with local cache and VersionNumber statement. The advantages are:

- central location of scripts

- very good performance if "VersionNumber" is used

- it is always available if the SAP system is running

And the configuration (with RFC User + password, guixt.ini file) is not too complicated.

There are also large installations ( thousands of users) that work with local scripts. 

Other central servers for the scripts (network, http/ftp) have the slight disavantage that they might be unavailable while the SAP system is running.