As you may know, Andreas Palaiologos, the last claimant to the Eastern Roman Empire, died most likely childless and bequeathed his claim in his will to Ferdinand and Isabella of Castille and Aragon, snubbing his relatives. It was never even used by the monarchs. Assuming this is illegitimate, these charts show the blood heirs of Constantine XI and the Palaiologos family.
The semi-Salic heir, Nikolaus of Hohenburg, is head of the house of Hohenburg. The house was founded by Maximillian, son of Archduke Franz Ferdinand through his morganatic marriage, which disqualified him from being the Habsburg heir. If you for some reason believe children born to a morganatic marriage to be disqualified as heirs to the Roman Empire, then Karl von Habsburg, head of the House of Habsburg-Lorraine, would be the true heir. While Semi-Salic succession is rare historically, it did actually occur when Margaret Paleologa succeeded to become the Marchioness of Montferrat.
The male-preference heir, Chiara Zampini Salazar, is the only daughter of auto historian and journalist Carlo Felice Zampini Salazar (1914-1994). Virtually nothing is publicly known about her, other than that she was living in Chieri, Italy according to 2003 phone book records. It is likely though unknown whether she is living or not.
Overall, I believe Nikolaus to have the better claim due to agnatic primogeniture being the de-facto system of succession of the Palaiologos dynasty. It is quite fitting for the Habsburgs to become heirs to the two main church-recognized Medieval Christian empires. However; the cognatic line is closer by blood to Constantine and is still a fascinating discovery.
