Yevamot 39B

אית דאמרי: בביאה, כולי עלמא לא פליגי דביאת קטן עדיפא. כי פליגי בחליצת קטן.

There are those who say that the dispute is more limited: When there is the possibility of consummating the levirate marriage, everyone agrees that the consummation of the levirate marriage by a younger brother is preferable to the ḥalitza of the eldest brother. When they disagree it is with regard to the significance of the ḥalitza of a younger brother.

והכי איתמר: חליצת קטן וחליצת גדול, פליגי בה רבי יוחנן ורבי יהושע בן לוי. חד אמר: חליצת גדול עדיפא, וחד אמר: כי הדדי נינהו.

And this is how the dispute was stated: R' Yoḥanan and R' Yehoshua ben Levi disagree with regard to a case in which there is choice between the ḥalitza of a younger brother or the ḥalitza of the eldest brother. One said: The ḥalitza of the eldest brother is preferable. And the other one said: The two options are equivalent.

מאן דאמר חליצת גדול עדיפא ⁠— דהא מצוה בגדול. ואידך ⁠— כי אמרינן מצוה בגדול לענין יבום, אבל לענין חליצה ⁠— כהדדי נינהו.

The Talmud explains: With regard to the one who said that the ḥalitza of the eldest brother is preferable, this is due to the fact that the mitzva of levirate marriage and ḥalitza is incumbent upon the eldest brother. And the other Sage would respond to this claim by saying that when we say that the mitzva is incumbent upon the eldest brother, that is only with regard to the consummation of the levirate marriage; however, with regard to performing ḥalitza, all the brothers are equivalent.

תנן: לא רצו ⁠— חוזרין אצל גדול. מאי לאו: לא רצו לייבם, אלא לחלוץ. וקתני: חוזרין אצל גדול, ושמע מינה חליצת גדול עדיפא!

The Talmud suggests a proof for the first opinion: We learned in the Mishnah: If the younger brothers do not want to consummate the levirate marriage, the court returns to the eldest brother and demands that he at least perform ḥalitza. The Talmud suggests: What, is it not that the other brothers did not want to consummate the levirate marriage but are willing to perform ḥalitza? And yet the Mishnah teaches: The court returns to the eldest brother so that he can perform ḥalitza. If so, conclude from here that the ḥalitza of the eldest brother is preferable.