In every episode in the Fullmetal Alchemist: Brotherhood series, about halfway through the episode there is an interruption in which two images (eyecatches) with characters are displayed.
Which characters are featured and how many times?
I will refer to the first eyecatch of each episode by the number of that episode suffixed by the letter a, and to the second by appending the suffix b.
I have considered the names displayed along the images for this count. Thus, some characters may appear more than once referred to by different names, like King Bradley and Wrath (since these may be regarded as alter-egos), and some may only have reference to the fact that the name appear shortened or something similar, like Winry and Winry Rockbell. The only debatable choice is that I differentiated between Greed in his first body and in Ling Yao's body. But then again, you just need to add one to your count if you'd rather count them as only one character (since Greed only appears once in his first body).
The list follows the order of first appearance, appending the number of the episode a character may have been re-featured after the name.
The number of times each character that is featured more than once appears, in decreasing order:
Edward Elric is featured 10 times, Winry Rockbell 9 times, Alphonse Elric 7 times, Roy Mustang 7 times, Scar 5 times, Alex Louis Armstrong 5 times, Olivier Mira Armstrong 5 times, Van Hohenheim 4 times, Greed (in Lin Yao's body) 4 times, Riza Hawkeye 4 times, Solf J. Kimbley 4 times, Tim Marcoh 3 times, Maria Ross 3 times, May Chang 3 times, Shao May 3 times, Jean Havoc 3 times, Lan Fan 3 times, Envy 3 times, Pride 3 times, King Bradley 3 times, Sig Curtis 2 times, Izumi Curtis 2 times, Roa 2 times, Martel 2 times, Dolcetto 2 times, Ling Yao 2 times, Lust 2 times, Grumman 2 times, Selim Bradley 2 times, Sloth 2 times, Zampano 2 times, Jerso 2 times, and every other featured character appears only once.
This count may differ if one decided to count the number of times a character is seen, since some characters appear without being referenced by their name, like in the case of Roy's Team in the last eyecatch. If one decides to count those, one should add: 2 to the count of Maes Hughes (9a as Hughes Family, 10b back facing camera), 1 to Gracia Hughes (9a as Hughes Family), 1 to Elicia Hughes (9a as Hughes Family), 2 to Roy Mustang (10a back facing camera, 64b as Roy's Team), 1 to Envy (16a shadow can be seen behind Focker), 1 to Riza Hawkeye (64b as Roy's Team), 1 to Jean Havoc (64b as Roy's Team), 1 to Kain Fuery (64b as Roy's Team), 1 to Vato Falman (64b as Roy's Team), 1 to Heymans Breda (64b as Roy's Team) and 1 to Black Hayate (64b as Roy's Team).