vFox9 vs PHP+SQL...

They are different things.

PHP is a server side scripting language and SQL (I think you meant mySQL but doesn't really matter) is a service based data backend.

VFP on the other hand is a data centric language having a file based database engine of its own (and can connect to any backends). VFP can be one of the layers in a multilayered application or used as a single tier application.

It depends on what you want to do, what you know better and such factors.

When you say accounting program it might be a simple one that could be used with browsers and thus you could use PHP+mySQL, asp, asp.net with mySQL, MSSQL or some other backend, VFP with its own dataengine or any other backend. However if the application is not something simple to be tolerated as a web based application (technologies are evolving fast that in near future even serious applications could be tolerated to work with browsers - currently even simple things like this forum can turn out to be intolerable day to day) then alternatives are desktop and smart client applications, web services and such.

If my concern was making a choice about a language today and for a moment thinking if I were new to all these then probably I'd choose C#.Net (well I actually already chose C# as second to my VFP work) or Java. Decision is hard, there are tons of good technologies ( for example I like Phyton/IronPhyton too, my kid works with PHP+mySQL etc but I just don't have time to evaluate in depth and work with them )