I think by Embraer “small series” they were referring to the E-145 and its earlier regional turboprop predecessors. The E-170-190 type rating is valuable not only for the 175 but also for the 190s and would require only differences training for the newer E-2 series, although those are sort of scope limited in the US.

But yeah, right now today for employability A320 and B727 are the types to have worldwide. And of the two, the 320 is probably the best unless you aspire to SWA or Alaska, since upgrade to the 330 and 350 aircraft is pretty easy with minimal additional training.