A couple of points on this one. When I was in high school, I really wanted to attend the Air Force Academy. When I started the process with my Congressman, he sent me a form letter with the four establishments that go through the Congressional Nomination process, and to indicate, in order, those that I wished to attend. Of course USAFA was first, then I thought and put USNA second. I certainly didn't think that I would like to go to West Point, so I left USMA blank. At the end there was the spot for USMMA. I didn't even know what it was at that point. I asked my dad, and he said it was the Merchant Marine Academy, so I put it as No. 3. Long story short, I was nominated to all three, but appointed to USMMA. To be honest, I don't know that I would have been happy with the other academies. Not so much with the programs, but most likely the 10 year total commitment to the military. When you are 18, 10 years is quite a long time. I sailed for many years after I got out of school and still work in the maritime industry. Ironically, that will make 30 years this year. And that doesn't seem very long at all.
I don't know if having the attitude of "which college is easier" is really the right way to go here (I apologize in advance if I am reading it wrong). All academies are rigorous. The Plebe system is not a pleasurable experience, and is pretty much the same across all of the academies. At KP, they do not have the luxury of a protracted indoctrination period since the time at school is limited to three years. As far as an overall career choice, I WOULD say that KP would be the best alternative of the service academies, if only for the options available to the graduates. What other academy has graduates that can serve in the civilian industry, or in the branch of the military that they choose?
As far as KP not being a military academy? Well, I don't think things have changed that much since I went there, and it was certainly a military academy. We all did graduate with commissions, after all.
Jasperdog has is right. Plebe year is a real grind and weeds out quite a few people. Sea Year makes up for quite a bit of what goes on at the academy. At least it did for me.