The Rabbeim
The Rabbeim always tried to make the Brocha on a Calabria Esrog. They used an Esrog from Eretz Isroel to do extra nanuim.
The Rebbe Rashab and the Frierdiker Rebbe used to receive the Esrogim from the Kreh family.
When the Frierdiker Rebbe came to America he received his Esrogim from Rabbi Jacobson.
Throughout all the years, the Rebbe always made a Brocha on a Calabria Esrog which was cut under the supervision of Rabbi Jacobson and then Rabbi Lazar.
Many people brought Esrogim to the Rebbe, some from Israel and from the fields that were planted from a branch or a seed from a Calabria Esrog. However, when the Rebbe was asked by one who brought an Esrog from Eretz Yisroel as a present if the Rebbe made a Brocha on his Esrog, the Rebbe avoided answering.
Rabbi Jacobson and later Rabbi Altein used to give the Rebbe many Esrogim, up to 50. The Rebbe used to check each one, keep some for himself, his wife and his mother, and give most of them to specific people or communities.
Each year Rabbi Jacobson, and later Rabbi Altein, received a loan from the Rebbe of $500, this in addition to the payment that the Rebbe made. Rabbi Jacobson wanted to be a servant of the Rebbe, so he requested that the loan should be of $501, as the posuk says: "Eved Loveh Leish Malveh".
The Rebbe checked the Esrog with his glasses but not with a magnifying glass.
The Rebbe always gave a big Yasher Koach for the Esrogim.
The Rebbe wanted a big Esrog with a shape that is narrow at the bottom and becomes bigger on top, preferably with a pitom.
The Esrogim for the Rebbe were labeled with the letter ק that stands for Kodosh, until today the big Esrogim are labeled with the Kuf, in the belief that the Rebbe will bentch on one of these Esrogim. It should be this year!
The Rebbe generally paid for his Esrog after Sukkos, around Chanukah. Just in 5750 the Rebbe paid before Sukkos. (See Hisvaduios Toras Menachem 5710 page 85).