What ever you are using for regular valves should be fine for the master.

The idea behind a master valve isn't that you try to get a "more reliable valve". The idea is that two valves have to fail before your system wastes water.

I am also trying to install a master valve for my new system.
Where do you put a master?
Before backflow preventer or after?
Should I put it in a separate valve box from the first manifold?
Any comments would be appreciated.
Thank you.