The smallest buses, which seat 9-12 people are called combis. Strictly speaking the middle-sized buses are called micros or custers. Personally, I tend to refer to every Ruta Recomendable as a combi, regardless of the size of its buses.
Most of the Rutas Recomendables have two staff: a driver and a cobrador. The task of the cobrador is to collect the fares and to open/close the door. The cobrador also shouts the names of the avenues the combi will pass. This is often incomprehensible.