If you're using MySQL, php is fine. I just didn't say php for two reasons 1. You didn't list it in your first post 2. I wasn't sure what kind of database you were going to use.
If your using a MySQL database, PHP is perfectly fine. It's plenty easy and simple. So it's really up to you. Whichever you feel most comfortable with. Although, I will say this; if this program you're making is going to be based offline (meaning on local machine and not a server/website) then I'd use C#. If it's going to be web-based I'd use php. Unless the server you're using supports ASP.NET, in that case you can use C#.