ŝarĝaŭto

Read it and you have it. Ŝarĝo is a load; aŭto is a car. A ŝarĝaŭto is a load-car: a vehicle whose job is cargo rather than people. Four syllables, two diphthongs, ŝar-ĝa-ŭ-to collapsing to ŝar-ĜAŬ-to in practice, and no dictionary needed. This is the language doing precisely what it advertises.

So which one do Esperantists actually say? Both are correct and both are in use, and the honest answer is that the borrowed one has won the frequency contest. Kamiono sits at rank 2,269 in this course's list and ŝarĝaŭto at 2,875 - six hundred ranks behind it, on the same corpus. ReVo gives ŝarĝ- a full entry and mentions ŝarĝveturilo as the general cargo-vehicle term without granting ŝarĝaŭto a headword of its own, while kamiono has one. That is the usual shape of these contests: the international loan is shorter to say and instantly recognisable to speakers of half a dozen European languages, and the transparent build is the one a beginner can decode but nobody reaches for first.

Learn both, use kamiono when you want to sound like everybody else, and use ŝarĝaŭto when you want to be understood by somebody who has known the language for a fortnight. Neither is wrong. The same argument runs through aviadilo against aeroplano and half a dozen other pairs, and it is one of the more interesting standing quarrels in the movement.

The doublet note from ŝarĝi carries here. That page teaches the pattern ŝarĝi X per Y: the vehicle is the direct object and the cargo comes in with per. So you ŝarĝas la ŝarĝaŭton per sakoj, never the other way round. Malŝarĝi unloads it, senŝarĝigi relieves it, and ŝarĝveturilo is the umbrella word for any goods vehicle at all, lorry or van or wagon.

The rest of the fleet. Veturilo is any vehicle, kamioneto a van or pickup by the diminutive, ŝarĝvagono a goods wagon on the railway, and the driver is a ŝoforo or, specifically, a kamionisto.