Excellent post by Maintain and he covered pretty much every point, but I want to add one important consideration scholarship conditions and a few follow up points. Scholarship Conditions:
I see Chapman requires a 2.9, Southwestern a 2.7 etc. I imagine like many incoming 0L's you believe obtaining those GPA's will be a piece of cake. Law school however, is very different due to the strict curve and at many schools you need to finish in the top 35% just to have a 2.5 G.P.A it varies from school to school, but there is a strong chance you will not maintain the scholarship years two & three. This is nothing against you personally, but the reality is everyone in law school is smart, hard-working and motivated and 100% of students think they are going to be in the top of the class, but 50% of them will be finishing in the bottom half and 25% in the bottom 25%. This New York Times Article does a far better job explaining the situation than I can. http://www.nytimes.com/2011/05/01/business/law-school-grants.html?pagewanted=all&_r=0
Personal Feelings about School:
It sounds like you have done the important process of visiting the campuses you are interested in and it seems like you are a person that does not enjoy downtown S.F or Downtown L.A you want a smaller environment, which is fine . Chapman provides much more of a college feel and you appear to have enjoyed your visit and that is very important. Each student has their own personal feelings about schools when I was visiting there were some I hated and others I loved, but you could have the opposite feeling. I liked Southwestern, because there was so much going on and Chapman felt isolated although the campus is beautiful. Nothing wrong with having your own preference this is a 3 year, $100,000 commitment so list to your gut. It sounds like Chapman left you with a good impression and the other schools did not. That says something about what YOU want and this is your life. Do not let anonymous internet poster like myself, a for profit magazine like U.S. News, or anyone else that knows nothing about you tell you what is best for you.
You mention talking to students etc at Chapman should be taken with a grain of salt, but I think those opinions should carry the most weight. Every posting on this board or other law school boards is behind a computer screen and you have no way of gauging our credibility. I could be a crackhead in a public library there is no qualification for posting on the internet talking to students, professors, and walking around the campus is reality and can offer far more insight than the internet. District Attorney Reality:
Maintain also makes a great point about D.A's there are very few positions and even if you get hired as D.A. the reality of it is a lot different than what is displayed on T.V. and many people end up not wanting the job. So as Maintain suggests keep an open mind, but if you really want to be D.A. if you graduate from an ABA school it can happen, but just be 100% sure that is what you want. Choosing a School :
To answer your question I would negotiate with all of these schools for better scholarship terms more money and better conditions. Worse case scenario they will say no, but nothing bad will happen by asking.
This is also a pretty good article explaining factors to consider when choosing a law school. http://www.legalmatch.com/choose-the-right-law-school.htmlConclusion:
Knowing nothing about you it seems like Chapman is a good fit for you. Do not make things more complicated than they need to be, but I do encourage you to negotiate for better scholarship conditions and money you have nothing to lose and everything to gain by doing so.
Good luck in your legal career.