I flew Seneca 2s a long time ago both pax and freight as well as Aztecs as FM did.
I have to say from a purely practical point of view and depending on what you intend to carry the Seneca is easier to load through the rear port door whereas the Aztec only has the one door. We removed the club 4 seats and had spreader bars inserted in the Seneca and could take quite bulky AOG spares for various airlines. I don't think we could have wiggled some of those spares into the Aztecs. Just a thought.
Don't think there is much to pick and choose otherwise both aircraft fly well within their limitations.