Republic
Why on Earth would there still be things like kings and queens? I should be quite obvious by now that there is no divine mandate to have some random guys that may or may not be suited for a job that affects a ton of people, which didn't choose the fella in question to represent them.
I'm not only surprised that such a system would exist, but astonished that main political parties would even refuse to consider other options. And this comes from the PSOE doing it so now. The funnily called “socialist” and “worker” party. Not that any party would have an excuse to sustain such a contradictory system, mind you, but especially atrocious that such a party would go to those extremes to keep the system.
Said otherwise: fuck off.