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There is nothing wrong with any of your cars. that smell is a byproduct of the sulfur that is in the fuel............all fuel. Changing brands will not do one bit of good. For a little knowledge of how a modern ecu in a car works... 99% of your driving is done in whats called "closed loop" mode... the ecu looks at airflow from the mass air sensor, estimates the engines fuel requirements by plotting airflow, rpm and engine load on a preset fuel map and opens the injectors for that set amount of time... it then looks at the data from the oxygen sensors to see how completely burnt the fuel was - the more burnt it was, the leaner the mix, the less burnt, the richer the mix... it measures the oxygen content in the exhaust to do this, and it is looking for stoichiometric, which is 14.7 parts air to 1 part fuel ratio... anything below this is rich, anything above is lean - lean is good for fuel mileage, but not so good for keeping an engine healthy... once it sees how good the map was at estimating fuel requirements, then it modifies it... typically it will shoot rich, see if it was rich, then it will shoot a little leaner, see how well it does, then rich, then lean - its almost impossible to get it perfect every time, so it bounces from rich to lean pretty consistently... this is why an air/fuel ratio gauge bounces back and forth while at idle or cruise... Now....for those times when you want to smoke the Beamer or Benz next to you, (1%) of driving is done in whats called "open loop" mode... this is reserved for high amounts of throttle or wide open throttle... here, the computer abandons the oxygen sensor readings and only looks at the airflow and its preset map... because oxygen sensors are only accurate at stoichiometric (unless you have a wideband, which most cars do not come with from the factory), the programmers of the ecu decided that to save the health of the engine, they would shoot for somewhere between 10:1 and 12.5:1 for high loads on the engine....ok, so, open loop, no feedback from the oxygen sensors because we are operating outside of their accuracy range... also, a byproduct of this is that unburnt fuel makes it through the engine, sometimes to be somewhat reburnt in the catalytic converter making it get real hot... so, real hot catalytic converter plus sulfur in the unburnt fuel equals bad smelling exhaust, rotten eggs, to be specific... It is not bad and it is not going to hurt anything - high temperatures can actually help keep a catalytic converter free from contaminants.