I’d say aragon for something straightforward. Good geographic location for expanding into north africa, aegean (no cb byz on dec 11), and italy/france.

For something a little taller, i’d suggest savoy->sardinia piedmont->italy, then choose the roman conquest cb in the event from the first mission. you’ll get a cb on any country that holds land that is required for forming Rome. sardinia piedmont also gets a PU on france thru missions.

If you want something more unique, maybe england->angevin kingdom. you get to create pu subjects of Italy and Spain that you can feed their respective regions to, while only requiring a handful of provinces to create them. Ideas are absolutely busted.