Hey man, let me guess, being on the giant cutter as a nonrate completely sucks and now the idea of chilling at a sector as an OS for the rest of your tour is starting to look appealing. Been there, done that. Glad I did it. Being an OS at a sector is sweet. We are largely an ashore rate, meaning 80% of the billets are going to ashore.
I went to OS A-School recently. The classes are typically 13-16 people. I can tell you that every class while I was there had about 10-12 land units, and then 2-3 cutters. Mostly land picks as you can see. Something to keep in mind with OS is that many people are either boot-to-A or people in your situation, meaning that while some people may want a cutter, it's pretty typical that everyone wants those sectors.
With that being said, the picks process at OS A-school works like this--they don't take into account sea-time, time in service, performance at A-school, or any of that. The only thing they mentioned as maybe making a difference between you an another person when it comes to picks is time spent volunteering in the community.
Regardless, they have you rank the picks you want from first to last, and they make every attempt to get everyone something in their top five. So if you rank all sectors you have a good chance of getting one. Keep in mind though, if no one puts any of those couple boats at the top, it's going to be a crapshoot who they give them to. This where writing persuasive comments about why you want a certain billet can make a huge difference. Something else to keep in mind is that some boats can be male/female only billets, so that could increase your chance of getting it.
Generally, and in the case of my class, everyone pretty much got the billet they wanted and one person went to a cutter they didn't want, but they also did not rank that boat last either. My advice is if you really want to be on land, be willing to go anywhere and you're almost certainly get it. If you rank all the coolest, warm-all-the-time sectors in your top 5, you're going to be competing with everyone else in the class for those picks. Put some random sector no one really wants at the top and be the only person to put that #1, it's guaranteed to be yours.
Hope that helps.
Hope that helped.