It's worth looking up the histories of the heirs in question
, but you should consider also not just how the new Emperor might treat foreign nations, but by how their election might cause unrest and weaken the Empire itself. There's no good
option for the Fed here, but just varying degrees of bad.
Merimeth Sarum is right out as an option, as he is rather young, impetuous and very eager to both prove himself and break out of Jamyl's shadow. An Emperor Merimeth would be a champion of the Reclaiming and a very bad turn of diplomatic relations with the Fed.
Yonis Ardishapur is also patently not good for the Fed, being a highly-devout religious conservative. He is both intelligent and highly popular, and could easily bring the Empire into a new state of unity and strength that could be turned outward against the Empire's enemies, but his election would also cause friction with the newly re-integrated Khanid Kingdom.
With Articio Kor-Azor, he was closely allied with Jamyl's reign (even serving as Imperial Chancellor, the #2 spot in the Empire's hierarchy). He has a long history of carelessness, mental instability, sadism and violence. Most of it has been suppressed since his cleansing torture, but it's unlikely that it did much to help his sanity, despite what his public change of behavior suggests.
Catiz Tash-Murkhon is the least interested in warmongering, and most likely to encourage peaceful relations with the cluster at large. Her Udorian ancestry is a point of controversy among conservative Amarr, but she is the embodiment of what a progressive / liberal Amarrian Empire could be, but her family's extensive trading links and contracts with the State could be problematic for the Fed.
Uriam Kador, like Catiz, has had several progressive initiatives to modernize his realm, and could be well-disposed towards foreign powers. I don't know if anything ever actually came of Kador's personal invasion of Ratillose, or if it was just CCP derping, but it weakened his standing in the Empire and put him at odds with the Sarum.
Finally, there's Garkeh Khanid, a man so narcissistic that he became the only Heir in history at that point to defy millenia of tradition and choose his own life over his religious duty, and successfully rebelled against the Empire. Despite being brought back in "no harm, no foul", and given all his rights, status and privileges back, an election of Emperor Khanid would undoubtedly cause substantial internal turmoil within the Empire.