Oilcooled Pickhill/oxfords seem to last longest years-wise... maybe because there are few mechanical parts... maybe because they're an old design and most were built/sold before industrial MIGs were about.... still wouldn't have one in my shop again though.
My observations, in order of how I see their importance:
1. Machines by quality brands last longer than cheap tat.
2. Industrial quality machines last longer than hobby/garage welders.
3. Maintained and well-kept machines last longer than unloved machines
4. Transformers, on balance, last longer than inverters... with a few outliers.
So a 3 phase Kemppi MIG transformer ticks all the boxes... and we have two of them at work, approaching 15 years old and welding as well as the day they were bought Maybe this is confirmation bias Since my Miller inverter MIG/stick is 24 years old and does the same.
I prefer inverters full stop, though. Certainly for stick and TIG.