But I think if you ask experts (philosophers of nature, people into foundational quantum mechanics) most of them would be many worlds proponents.

I finished my masters in a quantum computing lab. The reality is that most physicists just don't care about foundational QM, and stick to the Copenhagen interpretation. To me the Copenhagen Interpretation does not even count as a complete theory. It just stays very fuzzy on when wave function collapse happens, which makes it impossible to falsify.

>Questions: 'Which of the following, in your opinion, provides the best interpretation of quantum phenomena and interactions?'

in what do they mean by 'best'. For calculating and doing practical physics then sure Copenhagen Interpretation. But for what is the underlying reality of the universe you might get a different answer.

Copenhagen has an observer - your particle goes all ways through both slits deterministically following Schrodinger type stuff until 'the observation' when a dice is effectively rolled to choose one. But how do the laws of physics know the bunch of atoms far away is in the form of an observing physicist having a look? It would be cleaner laws of physics wise for them to ignore that, resulting in multiple observers seeing different outcomes. But for calculating, rolling a dice is easier.

That said probably Hilbert spaces are tools.