While you can take the luxury "cama buses" from Buenos Aires, it's about 16 hours and a long trip. It might be better to book a flight there to save time, then just take a taxi to the Sheraton. You can easily do the falls in two days. Keep in mind, US citizens need a Visa to enter Brazil so you will not be able to go to the Brazilian side without one. Don't be fooled by taxi drivers who tell you they can take you there. Some say they can get you a quick short term Visa, but it's wise to say no. We have had many discussions with people who have seen both sides and say it's really not worth the expense and time to get a Visa just to see the other side. Most of the falls are located in Argentina and you are not missing anything. Definitely take the boat ride as you will essentially be seeing everything that way. It's worth it!