QuarkXpress or InDesign for Desktop Publishing?

I am studying a Masters Degree at the moment and part of the course is a module in Desktop Publishing. We are using QuarkXpress at the moment. While I am still in education for the year I have the opportunity to purchase one of these packages at the education rate – substantial discount. However, I can only really afford one of them, so I want to make sure I get the one which will serve me better after college.
My main concerns are: What is the standard program used for Desktop Publishing?
Is there cross compatibility – if I am using QuarkXpress and need to exchange a file or items with another company using InDesign is that possible?
When sending files to the printers do they mostly just take PDFs or is there a preference for particular file types?

Further background – I am based in Ireland, and the type of work I would be doing with the software is mostly PR related (think newsletters, posters, flyers, brochures etc.)

Many thanks for your help.