Here's why it's difficult to determine:
* Subjectivity: Preference is a personal opinion. What one person finds more appealing, another may not.
* Variety of Factors: Preferences are influenced by many factors, including age, gender, cultural background, individual tastes, and even which characters or stories a person was exposed to first.
* Constantly Evolving Fandoms: Both DC and Marvel have their own distinct fandoms that evolve and change over time. What's popular today might not be popular tomorrow.
Instead of focusing on numbers, it's more interesting to consider:
* What makes each universe appeal to different people?
* What are the unique strengths and weaknesses of each franchise?
* How do the storylines, characters, and themes differ?
Ultimately, the "DC vs. Marvel" debate is often more about passionate fans expressing their personal opinions than about objective data.