By the EV (expected value) strategy, it makes more sense to take the shot at a million. The reasoning is simple: one has a 100% chance of a 200,000 euro payoff (average winning: 200,000 euros), the other has a 50% chance of a 1,000,000 euro payoff (average winning: 500,000 euros). The chance-at-a-million, on average, leaves you 300,000 euros better off.

However, the EV strategy is tailored to long-term gambling, not a one-off huge shot. This affects how one would act. I definitely deviate a bit from EV-based strategy when there's an unusually high-value hand when I'm playing Poker. To be fair, I'm not the strongest adherent to it in the first place (maybe I am subconciously, but I don't actively try to figure out my EV, even as a rough estimate) - I've given consideration to it when figuring out what my general approaches would be, but I don't think about it while actually playing in most cases.

Ultimately, I think in this case - I would take the 200k, unless I was already a millionaire (or close to it) at the time. Play it safe. I'm not sure what lower-guaranteed-amount or higher-win-chance I'd need to tip that. I would definitely take a 50% shot at a million over 1000 euro, probably over 10,000 euro. At 50,000 I'm not so sure.