In the many parts of the Filly world, there are several systems as to who is considered the leader of their location's Fillys, and how they are chosen. Choosing ones by royal heritage or the Filly with the most powers are common strategies, but that doesn't mean that these are the only solutions to do so.
This is not necessarily synonymous with a main line rarity, as some of them may be living somewhere else, are difficult to spot, or otherwise not the leaders of the place.
Emocia and Crystal Valley
Amor and Amanda of the Heart family are the rulers of Emocia, a rare case of claiming leadership while being parts of a regular 4-Filly household. Despite that Princess Jewel is Emocia's founder and often does ceremonial duties, she does not hold a position of leadership.
Filly Forest (location)
No Filly is known to hold a leadership in the Filly Forest (location). The restructuring canon of Filly Forest held the Forest as a meeting place for many horses to meet up in and do simple activities and to tell olden tales, while the first-release canon didn't even have a tangible location for the Fillys. All twenty Fillys are presumed to be standing on equal footing, but goes more by concensus and politeness as opposed to democracy or all-out anarchy.
The six parts of the Filly Kingdom are ruled over by different Fillys. The oldest and most highly decorated pair of Fillys, Emperor Karus and Empress Diva, rule the northern-most area of the Kingdom, and also host yearly parties in which all of the vast land's royals partake. Snow Queen rules the north-east area, and Sir Kuno rules the south-east area. Surefire cases can also be made for the remaining three parts, but nothing is explicitly mentioned.
Titania is the ruler of the Magical Land, being the oldest female member of the main heritage tree, and is known to be benevolent and wants all of her subjects to live a "happy and content life". She and her house also hosts an amazing ball on every full moon.
Magic is ranked as the Fairy King, but comes to the Magical Land only once a year and only for a visit.
Queen Cassiopeia is the highest-ranked Filly in Skylia, followed in rank by her housemate Princess Zodia. Because Cassiopeia travels around the Filly World a lot, Aries and Tauria holds the positions of vice-king and vice-queen.
There are no explicit rulership in Zimsala, and it is the only summer area in the Filly World besides the Filly Forest (location) in which no inhabitants hold royal titles. Abra and Cadabra does however hold a far bigger authority in Zimsala than the other inhabitants, having the most magic skills, most flashing outfits, and generally holds the leading word at such ceremonies as the cloak acquirement ceremony. The possibility of a meritocracy is present.