All these words refer to the same thing: the bus. But depending where you’re in Argentina, you’ll hear one, two or all of these words.
Omni, in Latin, means all, or for everyone, so ómnibus means a “bus for everyone”. You’ll hear this word coming specially for old people. Also, when referring to the bus station (Estación de Omnibus).
Cole is short for colectivo, and is usually used for buses running inside the city.
Bondi is a word for lunfardo. While traveling in Brazil, a long ago, I discovered that tram in Portuguese is “bonde” or “bondinho”, so I guess bondi comes from there. This word is mostly used in Buenos Aires, although is spreading. Here, it’s only used as cole or colectivo: for local buses.
Micro, in the other hand, is used to refer to long distance buses.
In some other cities of Argentina, things are different. In some places they call the local buses micros and the long distance ones, colectivos.
Anyway, doesn’t matter which word you use, people will understand what you mean, but I think is nice and interesting to understand this small differences.
– Es re tarde, ¡me tengo que ir ya o voy a perder el micro! (It’s very late, I have to go now or I’ll miss the bus!)
– ¿Qué bondi tenés que tomar? (Which bus do you have to take?)
If you say bus in Argentina anyone will get it, but be aware that we don’t use it.