Question in short:
is it more important to pick the advisor with whom you get along the best, or the specific area of research for which you are the most passionate?
More detail:
I've heard countless tales of "when you're in your 3rd year and everything is going horribly, to make it through, it will really help to have..." where ... is equally filled in with "a good advisor that you like" or "a research project that you care about and interests you".
I have already made a decision for a graduate school and am currently deciding between two advisors. To be fair, I like both advisors and both respective research groups, but one more so than the other, and vice-versa.
Professor A: I got to meet him, I agree with his philosophy toward research and grad students, I get the distinct impression that he will always hold my personal best interests as highest priority, and he is genuinely a good person. He is also extremely well-established in his field, tenured, and all his grad students like him and I seem to get along with them too. Fairly large group (~30 people)
Professor A's research: I find very interesting, but not my original motivating area of research back when I was applying to grad schools. He is also much more applied / inventory-like, as opposed to theoretical / research-scientist-like.
Professor B: Younger, well respected and somewhat established, but newly transferred up to my school, and therefore presumably will be working hard to get tenure (and also will be as new to the school as I am, regarding which courses to take, quals, and other advising areas etc.). I have a good initial impression of him, but frankly I know very little about him. He has only recently come under consideration and I will not get an opportunity to meet him in person or have extended interaction beyond phone calls before having to decide. Smaller lab (~8 people)
Professor B's research: Almost exactly what I was originally shooting for when I applied to grad school. Already a few interesting projects I may be able to work on. More theoretical in nature (although does include experiment), and more research-scientist-like.
All advice is greatly appreciated, as well as some context on what your background is and where you and your advice are coming from.