Is a well known program more likely to have better academically prepared students? Or is it safe to assume that graduate study on a whole requires students to be strong readers and able to give intelligent critique, even in lesser known state school programs? (I understand that strong programs with tiered funding are more internally competitive, and therefore not always constructive or supportive of fellow students either.) On a whole, how much do the abilities of the other students (academically and creatively) affect an individual's MFA experience?
I don't think it's safe to assume anything, BO. But as far as your first two questions go: There's no way to measure these things without calling up six students at each of your potential programs and asking them about the atmosphere and the level of student work. And that's a huge investment of time, and a huge annoyance for those students. Stick to what is measureable, apply to as many programs as you can afford, and then talk to students once you start getting acceptances.
The last question is a great one, and I'd have to say that your fellow students probably have the biggest impact of any factor in your MFA experience. You will hopefully make lifelong readers and friends. The whole small-program vs. big-program argument is related to this. Do you want a small, intimate setting, or do you want a lot of fellow students from which you might find a high number of simpatico people and writers? There's no clear answer, though I think the larger programs offer you more options.
You can't predict the level of writer/people for your incoming class, but you can talk with current/former students about the atmosphere of the writing community. Supportive? Competitive? A mix of both? There's obviously something to be said for both. I know I had the likes of Nick Montemarano, Susan Steinberg, and David Roderick who were constantly like "Here, read this book," or "Let's talk about this story," or "Don't listen to what those idiots said. Listen to your own voice," or "Hey, maybe you should listen to what those idiots said, because right now you seem really lost."
It's important to have and build that community around you.
Anyone who'd like to talk about the community (other writers and students) at their particular program, past or present, and how important that was (very much or not at all), please feel free to add your voice to the comments section. Rock on.