The "most beautiful" were the usual suspects.
Grand Duke Dimitri
Prince Felix Yussupov
Many Romanov men were very handsome in their youths but became excessively fat, thin, or dissipated when adults.
Victorians aged badly.
Grand Dukes Serge & Paul had unique personalities, were elegant, and when not too emaciated had supurb physiques when wearing Russian costumes.
Singular in allure and beauty were:
Grand Duchess Elizabeth
Princess Olga of Yuguslova
Marina, Duchess of Kent
Princess Alice of Greece
Princess Cecilia of Hesse
Grand Duchess Tatiana
The women in the Rumanian royal family were lovely when children.
Still, beauty and glamour can't best the mystique of the iconic OTMA. As historians point out it's virtually impossible to find a photograpgh of the four grand duchess' that is not uniquely charming. A feat when considering that OTMA's formal photographs make evident that their best features are their extraordinary eyes, translucence, and the details of their paper doll attire which is obliterated in the vast majority of their HAZZY candids. In informal shots the daughters of the Tsar wing it by the force of their distinctly expressive personalities and enchanting countenances. i.e., Innocence and charm without guile personified. Unfortunately, the gauze factor of most of OTMA's candid photos is a minus.
Qualifier. Anastasia is deficit the gracefulness that came naturally to her sisters. The youngest grand duchess has very fine eyes and regular features but she occasionally carried herself awkwardly and when posing for informal photographs squints, squirms, and grimaces more than was warrented. Arguably, afflicted with bird-in-a-cage syndrome.
Arturo Beeche's book "Dear Ellen" was entertaining (more photo albums PLEASE)--but he was blindsided when he lauded Queen Alexandra's "legendary beauty" but dissed; "Many considered Elizabeth Fedeorvna Europe's most beautiful princess. Of course our conception of beauty has changed MUCH since then." Granted, everyone takes an occasional bad photograph, but as depicted in clear formal shots the Grand Duchess Serge's features are singularly exquisite. A work of art--absolutely unique. By contrast, Queen Alexandra's looks are merely above average in beauty. The same is true of the Empress of Austria, although the later chose her clothing well and wore them magnificiently as did the Grand Duchess Elizabeth and Alexandra losifovna, the mother of Queen Olga of Greece.