It depends on what's important for you. What are your plans and goals.
QR: 320 has quite tough rosters, pay is quite nice but for a young single guy there are more fun places than Doha. You will most probably not get widebody within a year. Everything depends on the demand. Time to command on the 320 is not very long at the moment. Flying widebody for QR though, is pretty nice still.
EK: Dubai is more fun to live in, even if your long-term goal is not flying LH, the hours are always very good to have in the book in the future. Saving money might be harder in EK.