Hotel recommendations in Argentina, Uruguay & Brazil

I and my good wife are planning a 3-week trip to South America in April. Any hotel recommendations would be welcome for the following locations:

Buenos Aires
Colonia
Iguacu Falls
Salvador city
Rio

Additionally, if anyone could recommend a good beach resort + hotel within 2-5 hour bus journey from Salvador, it would be much appreciated.

Depends on your budget.
In Buenos Aires the Sheraton is great, but the Liberatador is superb.
But I've stayed in homestays for a fraction of either that were more fun.

In Iguazu (on the Brazilian side) you have hundreds of hotels, all very cheap.
We stayed in the first place mentioned in the lonely planet. (Can't remember the name, 300m from the bus station) Had recently been upgraded and was really good value.

Salvador City is a long way from the south of Brazil so I hope you are flying?
Again we stuck with the Lonely Planet and weren't disappointed.

In Rio try the Mango Tree Hostel. One block from Ipanema beach, the rooms are clean, modern and the staff are very friendly. Has en-suite doubles good enough for holidaymakers and dorms much better than backpackers are used to. The breakfast alone is superb.