Best method from Amsterdam airport to the Intercontinental Amstel?

Hotel is located on Professor Tulpplein on the Amstel River.

The Metro rail (or whatever its called in Amsterdam) should do the trick. There are Tourism offices all over that city, and they're legit too, so don't hesitate to go to one of the kiosks to ask for assistance.

Definitely think about getting a commuter rail pass while you're there, unless you're biking around.

If I understand their website correctly, you take the train to central station and from there a taxi costs 15 euros. Taking a taxi direct from Schiphol will cost approx. 45 euros.

Alternatively, when you're in Amsterdam you can take tram 6, 7, or 10 or metro/sneltram 51, 53 & 54 to Weesperplein, and then you're 300 metres from the hotel.

Have a lovely stay, it's a beautiful hotel!