When you search in google you will find hundreds of pages. Most of them are paid to be at the top of the list. Is the new advertisement. So the locals experts don´t have the chance to be visible and really help you in a more personalised way. Not all the people are the same and not all the people look for the same. Why dont you ask to a local expert in this field?
Just a summary after 20 years guiding in an independent way:
Day 1: Do a general sighsteeing full day. Depend on your budget you can have a commercial one for 4 hours in a touristic bus of 45 people with an unknown guide. Or you can get a private tour wich is more expensive but you will walk and enjoy the local culture. There are free walkings, there are lot of offers around. The law says that you must be with a legal guide with a credential. Besides that you will have quality tours or just boring tours. Depend on your budget again. The level of the guides are so huge. So depend if you want just a superficial sightseeing or if you want to enjoy and explore the local culture with an university degree tour guide and expert. Level of english also is different so you can have a fluent conversation or just the basic one.
Places you must visit in one day:
Pink House area. La Boca Caminito. Recoleta Cementery. San Telmo historical area. Other places depend on your schedule: Palermo Parks, Rose Garden, Puerto Madero, Coffee Stops, Museums like LatinArt, Evita, Jewish stops , Leather Stops, Wine stops, Coffee Stops, etc
If you have more than one day it will be wonderful! Buenos Aires is huge and need time to walk and explore so you can do :
Day 1 : South of the city
Day 2 : North of the city
If you have one day for the city only and more. I can recommend a typical 2nd day enjoying the Tigre Delta doing a Navigation. One time more you can do 4 hours commercial one or you can get a private guide and do a private tour with a shared 1 hour navigation to enjoy a relax day at the famous Delta
What about the nights? Dont hesitate to enjoy a dinner out with a tango show
What happen if I have more days? Better! there are much more things to do and explore. Like a day outside the city to enjoy the bbq, horses , and cowboys at a ranch. Or crossing the river to enjoy Colonia at Uruguay. Or just visit the museums or alternative areas!
And what happen if I want to spend a month at an apt? Please visit the 2 wonders in the world: Iguazu Falls and Perito Moreno Glaciar or if you like wine: visit Mendoza for the wine route tasting
Ask to a local expert tour guide to organize all at your style! A commercial person will try to sale. A local guide will try to satisfy your expectations!
Hope that helps. Hire me! http://guidesfinder.com/lizandrea-r/