Industrials.
Heavy Industrial Armor = Standard BattleMech Armor.
Advanced Fire Control = Standard BattleMech Cockpit.
Ejection Seats are for losers! :)
more importantly, industrials are standard rules level, primitives are obscure rule book.
Though to be serious, it might depend on tonnage. light/medium units might get hit less on engine, so primitive is more effective. heavy (at least faster heavies) and assaults, the engine size hurts. I haven't look to see where that might actually break. But you can't have a 4/6, 100 ton primitive (would be a non-existent 480 engine?), so I know an industrial is better in that one case :).