Either your first or second choice should be fine as far as flat resistance (The Contis or Schwalbes). The Schwalbe Marathon Plus is going to be super heavy, but also seems to be the 'gold standard' (if there is such a thing) as far as flat resistance goes. As others have said, wider is better for gravel. How wide you need to be safe is more a function of your bike handling skills. 28 is way better than a 23, but 32 is still better for gravel. 35 even better.

I have Conti City Contact (not sure if they're no longer made, renamed or what, but I can't find them on their site) in 37 on my hybrid. These work great on all road surfaces, as far as flat resistance and handling. I have Vittoria Randonneur Pros in 32 on my Jake. They are not as good on larger gravel, but they're still acceptable. Actually, they're quite good, just not as good as a wider tire.