I expect you'll find partisans of both sights here. My personal take -

1901 sight -

• Finely adjustable.
  
• Adjustments inconvenient.
  
• Usable aperture that can be effective after enlargement.
  

1902 sight -

• Semi-fine adjustable elevation, fine windage.
  
• Adjustments convenient
  
• Aperture not well-defined if enlarged to usable size.
  

Those who prefer notch sights are probably best served by the 1902. Those preferring the advantages of a usable aperture should find the 1901 more useful.