לא נמצא פסול בעמר ובשתי הלחם ובלחם הפנים "Never was a blemish found in the 'Omer, the Shetei HaLehem or the Showbread" (Aboth 5:8). Rabbenu the Hida, z"l, asks in the name of the Binyan Yehoshuwa', z"l, how it is that, in all Shas, the 'Omer and Shetei HaLehem (which are the two breads offered on Shabu'oth at the end of the 'Omer), are mentioned before the Lehem HaPanim (the Showbreads). The 'Omer and Shetei HaLehem occurred once a year, whereas the Lehem HaPanim was every Shabbath and we have a concept that what ever occurs regularly, goes first (Tadir WeShe-eino Tadir, Tadir Qodem).
He answers that the 'Omer and Shetei HaLehem have a slight additional holiness vis-a-vis the Lehem HaPanim. As a result, there is somewhat of a reason to mention them before the Lehem HaPanim.
Additionally, there is another significant difference between them. Both the 'Omer and the Shetei HaLehem have an offering connected with them, but the Lehem HaPanim does not require any offering. So, therefore, the 'Omer and the Shetei HaLehem have a reason to be mentioned before the Lehem HaPanim, even though the latter occurred more regularly.
(See Kissei Rahamim, Pirqei Aboth 5:8)
Pirkei Avot of the Chida, Pirqei Aboth, Hida