What lilmak said about how the fuel hits used to be is spot on.
When carrying 100% fuel, burning the main fuel tank first was POTW standing order. Why? Because if you took a fuel hit at all, it was almost guaranteed to be a main fuel hit. At which point you would use the 12min of aux fuel to finish the fight and make it home.
I find that the fuel hits are less frequent now, and you are just as likely to take an aux hit as you are a main hit. Now, I recommend burning the aux fuel first for better balance and plane handling.
As for the engine, I find that jugs are more prone to oil leaks, but less likely to take a total engine hit. There's kind of a tradeoff there.
Overall, I think the amount of damage the jug will take is the same, just more varied in the types of damage you take.