Open Source Contact Database Program ASP.NET And MSSQL or PHP And MySQL?

[altsounds]

I Am currently looking at building an Open Source People Intelligence Application (Fancy Word for a phone book) for my church..It'll basically be a database system where you can view info on a person and automate actions like send a "facebook message to these people on this date", "Generate a consent form for this person's parents" kinda thing..Lemmie give you some background..I've been working in .NET and MSSQLfor the last year and a half (Building small data apps for business) and i think im starting to get pretty good at it, My question is now im thinking of open sourcing this project should i plow on with ASP.NET or use Somthing Open Source like PHP (Also open to Python although the syntax looks bizzare, or rails, grails, practically anything apart from Lotus Domino =P) I am a fairly quick learner but am studying for a Microsoft Exam at the end of the year and have a lot of projects at work at the moment..Most people dont want a gritty my "my language is better than yours" debate but I Love them so go ahead!!It needs to be secure though cause it's real people's data!!Thanks-Daniel