I live near Malba. Yes, there is a villa behind Paseo Alcorta and a stable population of beggars on the corner of Salguero and Figueroa Alcorta (sorry, the word 'beggars' doesn't sound nice... pardon my non-native English) , but it is not unsafe at all. I have returned from Paseo Alcorta across the plaza next to Malba at night, no problems (on the other hand, my sister had her backpack stolen in that same place... but she gets mugged everywhere, so...)
Plus, sidewalks on Figueroa Alcorta (Malba) are wider (a plus if you have kids and want to ride their bikes without apologizing to pedestrians), spaces more open, greener. You have Jardin Japones, Plaza Alemania, Bosques de Palermo, KDT, Barrio Parque nearby. Club de Amigos is great if you are going to use it. If you live on Figueroa Alcorta you don't have cartoneros leaving a trash mess like they do on other areas.
The good thing about Canitas is that there is more of a "barrio" feeling than there is on Malba, more shops, more people. But being Argentine and knowing I'll be stuck here forever with all those people

, I prefer a bit of isolation, less barrio and more tourists, different faces, different languages.
You'll be fine on both areas, but I prefer Malba.