I was unimpressed with the AF lounge when I visited last September. The Alaska lounge is quite small, but they have a pancake maker which I do enjoy. The DL lounge is probably your best bet. Not good for food options, but they have a staffed bar (at AS, you have to ask the front desk agent for a drink) and there's a good amount of room to spread out with. The AF lounge has slightly better food than DL, but pretty barren lounge overall.

As a DM, you should be able to access it any time even when not flying. The fact that it's outside security makes it easier to access. You'd have to get through terminal 1 security for the AS Boardroom, and it's a different access point than DL terminal 1 so I doubt you could make it in.

I'm assuming you'll be on a domestic flight arriving at SFO terminal 1, then have to transfer to the international terminal. If that's the case, you'll have to leave security anyways, and the SkyClub is immediately outside security. Just as you exit the secure area, look to your left and you'll see a set of elevators on the other side of the escalator that goes down to baggage claim. Take that up one level and the SkyClub is up there.

Best way to get to the international terminal would be to go back down to the departures level, then get to the air train. Don't follow the signs by baggage claim. Instead turn left down the terminal walking past the DL check in counter, US Air, Frontier, etc. Then you'll get to the other security checkpoint. Take the elevator or escalator up 1 level, then the walkway over the street and you'll be at the airtrain.