So what are the options for public transport in Uruguay? Well, actually there are no real alternatives to bus travel. Trains are available to a limited degree for commuter services around Montevideo, but long-distance national services do not exist.
Due to the small size of the country, national air travel is not an option either. Formerly accesible services by the military air force are no longer available, and the national airline Pluna only offers flights to and from Montevideo and Punta del Este. The airport in Montevideo Aeropuerto de Carrasco handles mainly international destinations, and flights to Punta del Este are normally legs of international flights.
What is good news is that the bus system is extensive and generally works reasonably well. Buses leave on time and are reliable, with the two main bus companies Copsa and Cot providing frequent services throughout the country.
In the special case of going to Buenos Aires, ferries are a convenient and fast means of transport. You can combine bus and ferry travel or take a direct ferry from Montevideo, as described here.