Say you take a substituted benzene* and react it with oleum and nitric acid. Would it result in a nitrated ring, a sulphonated ring, or some sort of a combination?
Thinking about it in terms of the first step, the stronger base of $\ce{SO3}$ and $\ce{HNO3}$ seems likelier to get protonated first, making the preferred protonated electrophile (say it's A) less reactive than the other possible intermediate (say that one's B). But then the next step, the r.d.s, requires a pretty strong, reactive electrophile to attack the ring, which would make B the probable winner.
How do I decide between these factors, if such a general assumption can be made?
*I assumed a substituent wouldn't make a difference in this comparison. The answer, if so, would be more widely applicable than if the question were just about benzene. If there are differences, a note on them would be appreciated.