Buenos Aires has respected art galleries and contemporary artists coming onto the scene every year, plus plenty of art events to celebrate. Gallery nights is the easiest way to see it all. You choose a barrio you want to check out, and walk around the area, entering different galleries, art parties, artist chats and live music shows.
If you have limited time to see great art while in Buenos Aires, I would suggest just heading to MALBA, which has world renowned resident art and rolling exhibits, or MNBA to see paintings by Goya and Van Gogh. They are so close to each other you could experience both in one day. Do it on La Noche de Los Museos and it’s not a penny to you.