I think a 125cc two stroke dirt bike, while riding in the sand dunes lives a hard life...
However, as far as cars/trucks go, engine load and subsequent lifespan may not be self evident. A turbocharged 4 powering a large vehicle would seem at first to be working hard. However, using boost for power vs. RPM for power, create very different loads.
In very general terms:
High RPM stresses every component, cams spin faster, chains wear faster, piston rings travel much more distance over their lifespan, and so on. RPM can place far higher loads on rod bearings than boost. BMW's rash of rod bearing wear issues are proof positive of this. Continuous high RPM operation generally equals high rod bearing loads due to the inertia of stopping and starting the piston so rapidly.
Boost allows generally lower RPM operation, therefore the increased ring loading and valve + head gasket sealing are the issues to be addressed. Rod bearing loads are certainly higher at low RPM vs. a normally aspirated engine. This is rarely a problem, as those loads are often less than the rapidly cyclic loads of say, a 7000 RPM engine. Furthermore, most modern turbocharged engines have torque curves that drop off markedly at high RPM, managing rod bearing loads.
I'd say a vehicle with a very undersized, normally aspirated engine lives the hardest life in normal use.
