re: Which board game should I get for Christmas?

You'll be fine starting off with Intrigue, if you like it and have played through all the cards a good bit pick up the base game or the prosperity and seaside expansions.

There are two player variants out there for Catan but with no trading it's not as fun.

I think Agricola is actually a mich better game than Catan with more strategy and less luck. And you can play two player.

If you get Catan I think the Seafarers expansion is a must.