I wish I knew where everyone else was regularly finding challenging AI opponents.
The only thing I've noticed them do better since 1.3 is power management, so it takes a bit longer to crack the shields.
Combat Zones is where I generally find them.
People speak tales of RES still but all the times I gone have been boringly empty at most I get 5 ships spawn usually cobras and sideys.
Military Strikes probably work just as well but unless you are grinding merits probably isn't worth it financially.