Question: Computer Science PhD admit here. 

Is it crazy of me to turn down a top school (MIT/Stanford) for a lower-ranked school (think Cornell/UW/Columbia/Michigan) if I think there is better advisor fit?

Obviously all of these are fantastic schools and I am very lucky to be choosing from them. However, I felt like I got along really well with my would-be advisor at the lower-ranked school than I did at MIT/Stanford. People have told me that it's crazy of me to turn down MIT/Stanford since they are, along with Berkeley/CMU, on a different "level" than the other schools.

(My field is somewhat narrow so there is only 1~2 faculty at each of the schools doing research in the area. So regardless of which school I go to, if the advisor doesn't work out, I would be in a dire position.)

EDIT: Both advisors are well known in the field (and both have produced outstanding graduates), but the MIT/Stanford professor is good deal more senior. Also, talking with their current students, the MIT/Stanford professor is known to be pushy and have a "strong" personality (which may work for some people, but not sure whether it will work for me, as I've never worked with such people before).

Answer: 
There are some aspects of the decision that are independent of your advisor, such as having a large pool of impressive peers to learn from and work with, but the degree of fit with your advisor is certainly a major factor.

If you believe you can't work effectively with the potential advisors at the higher-ranked schools, then there's no point in choosing one of those schools. If the advisor at the lower-ranked school is performing at or above the level of the other possible advisors (as judged by influential papers and successful students), then again you don't have to worry. But your phrasing makes me a little uncomfortable:

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> I felt like I got along really well with my would-be advisor at the lower-ranked school
> 
> 
> 

This sounds like you are describing how quickly you clicked and became comfortable, but you can learn an enormous amount from someone even if you never develop an easy rapport with them or feel you could be friends. It's worth thinking about whether the less comfortable relationship could nevertheless be productive. Maybe it can't - it depends on the personalities and the details of your interaction - but it's important to distinguish how much you like the advisor from how fruitful the intellectual relationship might be.

I wouldn't stress out too much about this decision, though. My impression is that Cornell and UW are not so markedly far behind MIT and Stanford in computer science. (There's a gap, but not a huge gap.) If one of them feels like a better fit, you are not jeopardizing your career.
As previous responders have already answered, **both your options are top-notch institutions** and no sane future employer will think less of you for having gone somewhere on step lower on a league table. I know I can only present a single case, my own, but **beware of first impressions**! My worst advisor ever, who treated me worse than an unwanted brat, was oh-so charming and pleasant during the one-day interview and during our pre-employment e-mail contact. That said, my best advisor ever was lovely during the interview too, so all I can say is: Beware of first impressions! maybe the MIT guy just was having a bad stressful day? 

It is worth looking also at the **breadth of work within realated fields** at the two places too. It is not necessarily great if they are brilliant and have huge teams working on your subject, what would you be doing then? incremental work? if there is a breadth then you can expand and learn from experts in complementary subject too, expand your work and bring a fresh view or implementation for it? Not that I know what you are working with, but it helped me in material science.

Final point: **It's not only the Advisor that counts**. Did you get a chance to talk to others in the dept? it can help to get a feel of the collegiality, how friendly, open and helpful a place is it? or is it super-competitive? Also what are their pet peeves? do they struggle to get instrument time? (or whatever the equivalent is for computer scientists) do they ever get to present their work at significant conferences? 

I know this makes for an impossible spreadsheet, you might end up flipping a coin. If you're being offered a place at both MIT and Cornell, you must be a smart dude or dudette! I doubt you'll struggle to get a new place if the first one turns out to be impossible. It is allowed to quit. Worked for me. Then I took a year off to milk cows (über-cool!) and now am happily back in the lab at a better uni than I started :-)

**EDIT::** As previous responders also said, dont' forget the rest of life too. Don't move somewhere you don't want to live. **Friends, family, hobbies**, and/or the ease of travelling to fun places or home at weekends and holidays counts for a lot too! Remember, you'll be living there for at least a couple of years.