The "obsolete"-ness of CGI is really only a factor if you are doing big, complex sites with lots of page views.
Many people push the idea that CGI is obsolete don't really understand what CGI is. There is a widespread misconception that CGI is an inherently Perl-based technology. Many people attack CGI as a way to pad out cultic attacks on Perl in support of whatever language they support. If you want to be a real technologist, you need to understand the fundamental issues and make a choice based on the facts of the situation.
CGI is an interface with a webserver that allows you to write interactive pages in any language--even befunge. When a server gets a request for a page controlled by a CGI script, the server runs the script and returns the results to the requester.
If your programming language requires a VM, interpreter or compiler to load each time it executes, then this start-up time will be required each time your page is accessed.
CGI accelerators like FastCGI, mod_php, mod_perl and so forth, keep an interpreter/VM in memory at all times, may keep libraries loaded, and even cache bytecode from scripts to reduce script start-up overhead.
If you are making a simple, personal or hobby site, CGI will be fine. So will PHP.
If your site should grow to need a faster technology, you can move to mod_perl, FastCGI, or other CGI acceleration technologies.
What language you use should be determined by the tools it provides and how they fit with your needs.
- Make a list of the capabilities you need.
- Make a list of deal breakers.
- Now check each of your possible toolsets against these two lists.
- Which one comes out the best? Test it.
- Does it suck? Cross it off your list, and go back to step 4.
Also, I recommend against using befunge. Just because it is possible, it doesn't mean you should use it.
Update: As mpeters points out, mod_perl, mod_php, mod_ruby, et alia are much more than mere CGI accelerators; they provide access to the Apache API. They act as CGI accelerators, but can do much, much, more.
FastCGI is a pure CGI accelerator.
Update 2: PHP and CGI are not mutually exclusive. PHP can be installed as a CGI. PHP is often used with FastCGI.