Hi! I'm interested in experimental neutrino physics and wanted to give you my input. I don't know about U. Wash., but I visited Irvine and UNC as well, and for the most part liked both of them. If you have any more questions that I can answer having visited them feel free to send me a private message.
Have you visited these schools? I think that should be a big factor in your decision. Irvine, Seattle, and Chapel Hill are all very different in terms of the climate and the setting. Washington can be rainy, but it is beautiful in the late spring, summer, and early autumn. It's also basically a part of Seattle, so you can be close to a big city. Irvine is nice year-round, maybe a bit hot in the summer--you also don't get seasons in Southern California the way you do in other places. It's close to Los Angeles, but it doesn't feel like it's part of the city as all. Irvine is much more suburban, but that means there's also less to do socially. Chapel Hill gets seasons, but the winter's aren't that bad. I don't know about the summers there. It's a small town, but also more of a college down, so there's lots of places for students to go who want a social life.
Aside from the location, if you visited and met professors, that should have a huge impact on your decision. Find someone who think you would get along with well.
As far as ranking goes, from what I understand, the top 10 matter, but it is much harder to distinguish schools in the 11-50 range. A lot of the rank in this range has to do with the size of the departments. Even if you disagree with that, be aware that the ranking of the department is separate from the reputation of the physics faculty in the area you're interested in. A low ranked school can have well-respected faculty in the area you're interested in. At this point I would disregard the rankings of the schools you're considering.
What's more important is the faculty's reputation. Look at the papers published by faculty and graduate students at these schools. Look at where these advior's students have gone on to do post-docs following their doctoral program. However, I'm pretty sure students in all three groups have gotten great post-docs, so it will be hard to make a wrong decision.
Another thing to consider is whether you want to do hardware, simulations, data analysis, or all three. Make sure that the experiment you want to work on provides you with the opportunities you want. If an experiment is finished with construction and just taking data, you may not get hardware experience working on that experiment, whether that is good or bad is up to you.
Super-K is probably getting upgraded within another year or two, so there would be plenty of opportunity to gain hardware experience there. There also is a ton of data collected, so you would not have to worry about not having data to analyze.
Majorana is finishing construction of the demonstrator now. So you'd have data to analyze from that, and then you'd also be able to work on scaling up from the demonstrator to the larger detector. You'd also probably work with data from the full detector prior to finishing your thesis.
Also, Super-K is in Japan so you'd likely go there for some amount of time in your stay. Majorana is in South Dakota. That's important to consider as well, do you want to spend time overseas or would you rather stay in the US?
As I said, I don't know about U. Washington, I did my undergrad at a small school in Washington and didn't apply there because I had had enough of the rain after four years there. You could send an e-mail to John Wilkerson and ask him how he compares UW and UNC, I believe he was faculty there before he left for UNC.
Aside from Majorana, UNC has Katrin (also Caliope and Malbek--not neutrino physics but also worked on by students of Reyco). Aside from Super-K, UC Irvine has CAPTAIN, ARIANNA, and some others further down the road.
I know this is a lot of information but in my opinion the following should be how you make your decision (in order):
1. How well you get along with professor
2. How excited you are about the experiment (also make sure the faculty have room for students, but I know this isn't a problem at UNC and Irvine)
3. The professor is well-known in their field (a.k.a. their students get good post-docs)
4. The experiment is a good fit for you getting the experience you want out of a thesis project
5. You like the area and could see yourself living there
6. You are content with the department overall (courses, quals, requirements, etc.)