I've taken both, and while each test is challenging in its own respects, I'd say that the MCAT is definitely harder. Your post is obviously purely speculation with zero experience in taking or studying for the MCAT. Yes, everything on the MCAT is passage-based, but IMO, this actually makes the exam harder. Not only do you have to have good knowledge of all the material like you do on the DAT, but knowing that info isn't enough on the MCAT... you need to be able to extrapolate information from the passages and apply the correct equations/formulas/knowledge to answer the questions. And this all has to be done with proficiency and speed.
This is aside from the fact that the DAT doesn't cover Physics... that in itself is enough to give the "more challenging/difficult" title to the MCAT.
To the OP... the real question is who cares?!?!?!?? Most pre-meds are egotistical SOBs (moreso than pre-dents, but granted there are a fair share of us who fall into that category too), so they're going to fight you to the death when it comes to the question of difficulty between the MCAT and DAT no matter what you argue. If you're basing your career decision on how people view the prerequisite exam that you have to take to get into that field, you're setting yourself up for a serious tumble off a steep cliff... trust me on this one. Before you waste your time "sampling" both exams, I'd take some time to do some real introspective reflection about which profession you'd be able to devote your life's work to. Remember that at the end of the day, you're the one who has to deal with both the pros and cons of the career you choose to pursue... not the people in the peanut gallery. You're still young and you've got a lot to learn, but don't make this mistake...