My take is that alumni were more honest. Students are in the moment and completely in love the school they are at...they are in the honeymoon phase. They also have no experience with how their MBA is really viewed in the world and how the network has helped them. I had alumni tell me that other schools were better for my goals, no student really likes to admit that. Its not that students are dishonest they are just wrapped up in their school and really dont offer the most objective opinions.
I would say someone 2 or 3 years out is a great person to talk to...even better is someone in the industry or job function you want to pursue. One of the most helpful alums I dealt with actually was from a school other than where I am going. He also was one of the biggest promoters of Kellogg's management education, he did not work with alums but his company had used consultants numerous times and said Kellogg alums were among the finest. Thats not something a student at the competition would tell you. Someone in who is already doing what your goal is, is also is very helpful with applications because they can tell you what from their education is useful in their job...and that can help with selling how you need an MBA. Honestly the hardest thing for me was finding folks with MBAs in roles I want to be in...thankfully since I want something so specialized I got positive response regardless of where I was thinking of applying.
To add to what Kry said, alums can give you the full two year picture and then some. Students have at most 1 year at school and an internship come this fall when you reach out to them.
_________________
Kellogg Class of 2010...still active and willing to help. However, I do not do profile reviews, don't offer predictions on chances and am far to busy to review essays, so save the energy of writing me a PM seeking help for these. If I don't respond to a PM that is not one of the previously mentioned trash can destined messages, please don't take it personally I get so many messages I have a hard to responding to most. The more interesting, compelling, or humorous you message the more likely I am to respond.