- Obviously no list is "best". I'd say having them read the rules and then play with a veteran (or better, play online with a veteran by their side) is the best way to learn the rules.
Chapel - While not a rule, your friends need to learn about deck management. Mint would be a good substitute here.
Moat - Action/Reaction, defense for Saboteur or useful in combos with City.
Ironworks - a good Intrigue "choice" card. I also had the Island in mind when selecting this.
Saboteur - token attack card. Also chosen with Bridge in mind.
Caravan - Simple duration, pairs well with Throne Room.
Island - of the three "mats", this one has least room for error/misinterpretation by new players.
City - might as well teach them that letting the veteran get all 10 of these is a bad idea!
Quarry/Bridge - for learning about the changing values of cards (esp. with Ironworks and Saboteur in the mix).
Tactician - for combos, also to teach them to know what cards say (e.g. "If you discarded at least one card...")!
Throne Room - debatable. I'm big into combos :)
Added: If you're playing with Prosperity a lot, then I would replace City, Quarry/Bridge, Throne Room with Venture, Bank, Grand Market.