Navy2016:
You ask:
Has anyone turned down an appointment to USNA or USCGA for KP?
....
Has anyone else been in this situation in the past and felt like the right choice was made?
So 32 1/2 years ago I made the choice of USMMA over USNA and yes it was right for me. The majority of the reasons it was right for me are captured very well in Bruno's posted response and he offers a very good (surprisingly so for a Coastie - just kidding since as of right now USCGA is leading in the race for the Trophy...) list of why and why not to pick one over the other.
In regards to your post I'd add a couple of things... from your handle and your posts on these forums it seems that USNA has been in your sights for a long time and like many others USMMA has come into your field of view only recently. In your post you say:
"USNA- most selective,
KP- most opportunities"
Depending where you live USNA may or may not be the most selective/hardest to get into SA but if you have the opportunity to choose, I would say the prestige, real or perceived, of one particular Federal SA over the other should not enter into your decision process. At this point I'd continue to pursue an appointment to the Class or 2016 to all of the SA's you are interested in.
If you are trying to decide which one to indicate as your first choice to a nomination board, etc. then of course it appears you have a lot of ground to make up in accumulating knowledge about USMMA vs. USNA. If it's AT ALL possible, I VERY STRONGLY recommend an overnight visit to USMMA and I assume you've already been to USNA at least once, and may well have been to the summer program there. There are marked differences between the two places in terms of what it's like. The only way for you to really see and "feel" these differences is to go to USMMA and "live" with a current Plebe for the 20 or so hours an overnight visit provides.
As everyone here, including me, points out the USMMA does give you the widest array of options and opportunities immediately upon graduation. If you are indeed now finding yourself looking at those things and feeling you are no longer sure you want a long career as an active duty Naval Officer, but you still feel some sort of underlying pull to the sea and ships, then USMMA is definitely worth significant reflection and consideration. However as I say the differences are actually pretty profound and even though the USMMA may be easier for you to get into but depending on your academic interests and propensities it may well not be the easiest for you to "get through." I say this because there are two aspects relative to fit with your interests and abilities when you consider the decision in front of you - the fit relative to your expectations for your experience while at the Academies in question and the fit for your interests and aspirations following graduation.
Neither school will be easy to get through, nor are they really set up to be. They are both set up to train young men and women like yourself in support of their mission(s) and part of that is testing you in a multitude of ways both subtle and directly each day. In some respects, USMMA can be the most academically challenging because between the limited range of options for Majors and the fact the Sea Year means that a battery of four year's worth of degree courses are squeezed into your three years on Campus, it's never easy, though many of us Kings Pointers like to carry ourselves like it is. Another thing to consider is an aspect of USMMA that provides many of the options and improves the quality of opportunities immediately upon graduation is the Sea Year. For virtually everyone who gets through it, Sea Year is a great and useful growing experience but it's a time during which everyone does A LOT of growing up, so as interesting and fun as it is, there are moments when it is what it really is - work. It's that 1 full year of what is basically International Work experience that makes USMMA very different. However, I would say that if you wanted to that is something that you could also get and accumulate during the first 3 years or so of you post-graduate working life if it's something you want to do.
To me the big reason I choose USMMA over USNA was fit both while at USMMA - I wanted a smaller school experience, at the time the USMMA total student body was smaller than my big city High School and I was tired of "being a number" and I wanted to see the world so sea year "sealed the deal" for me; Post graduation I wanted to serve my country in some way but wasn't sure I wanted to do so as an active duty officer, as it turned out I stayed active in the reserves for 9 years and it was the right thing for me.
Good luck in your journey and quest.