Gemara

(Ula): Mid'Oraisa, a creditor collects Ziburis. "You will stand outside, and the borrower will give to you a security (from his house)." Surely, the borrower will give a low quality security!

(Rav Papa): The Halachah is, a Milveh Al Peh can be collected from heirs, but not from Meshubadim.

It can be collected from heirs, because Shibud is mid'Oraisa. Chachamim enacted that) it can not be collected from Meshubadim, since (there is no publicity to such loans and) buyers were unaware.

Kesuvos 97a - Question: If a widow sold land for food, can she take the land from the buyers to collect her Kesuvah?

Rishonim

Rif and Rosh (Bava Basra 82b and 10:49): The Halachah is that Shibud mid'Oraisa, for Rav Papa, who is Basra, says so in Kidushin.

Nimukei Yosef (DH Gemara): "He will take the security out" teaches that Shibud mid'Oraisa; the borrower's Metaltelim are Meshubad to the lender. The same applies to his land. Letter of the law, the lender can be Toref. The Rif and Ramban say that a Milveh Al Peh has no precedence (even if it is earlier) over a loan document. The property is considered to be Meshubad to the loan document, relative to a Milveh Al Peh, and a Milveh Al Peh does not collect from Meshubadim. Rav Hai Gaon says that an earlier Milveh Al Peh has precedence to collect, from the borrower or his heirs, land or Metaltelim that became Meshubadim Agav (along with) land. The Rashba agrees, because Shibud mid'Oraisa. The Rosh says that a Milveh Al Peh is collected from heirs only when we know that their father did not pay, e.g. he admitted just before he died. If not, they are exempt even from swearing.

Hagahos ha'Bach (2): This implies that according to the opinion that Shibud Lav mid'Oraisa, a loan document has precedence over an earlier Milveh Al Peh. Tosfos holds that Shibud Lav mid'Oraisa.

Rambam (Hilchos Malveh 20:1): If Reuven owed many people, the earliest debt collects first, from Reuven himself or from people who bought his land. If a later creditor collected first, we take the property from him.

Magid Mishneh: The Rambam does not distinguish between a Milveh Al Peh and a loan document. Whichever is earlier has precedence. The Ge'onim say that a loan document has precedence. The Rashba rejected their proofs; he holds like Rambam. Also Rav Hai Gaon says so.

Ramban (Kesuvos 90a): The opinion that collection of a later creditor is valid holds that Shibud Lav mid'Oraisa. A loan document or Milveh Al Peh collects only from Bnei Chorin, for we force the borrower to pay. We enacted that a loan document collects from Meshubadim, lest a borrower sell his property to prevent collection. This applies to buyers. There is no reason to enact precedence among creditors. If one creditor is deterred (from lending again, for he was unable to collect), the creditor who collected is encouraged. Also, one is unlikely to lend on condition that if he seizes he gets it, and if he comes to Beis Din he loses. The opposing opinion holds that Chachamim did not distinguish within Meshubadim. Alternatively, the other opinion holds that Shibud mid'Oraisa. The Rif rules that it is invalid collection.

Ran (Kesuvos 49b DH Kesuvah): The Ramban says that any debt that cannot be collected from Meshubadim does not collect from property Meshubad to a loan document. Therefore, if there is not enough property to pay a loan document and an earlier Milveh Al Peh, we pay the loan document. The Rif agrees in a Teshuvah. They learn from the Yerushalmi. It says that if a creditor comes to take the money for property that a widow sold (e.g. she sold for food for a year, but she receives money for one month at a time), she can say 'I sold for the Kesuvah' (its Shibud preceded your loan). If she would say that she sold for food, the creditor would get the money. Even though the obligation for food preceded the loan, since it cannot be Toref Meshubadim, a loan document comes first. The Bavli supports this. It asked whether one who sold for food can be Toref to collect her Kesuvah. If a Milveh Al Peh has precedence over a later loan document, the Kesuvah is no stronger than the Chiyuv for food. There would be no Hava Amina that she could be Toref!

Rebuttal (Rashba, brought in the Ran): Chachamim were lenient about food, to consider it as if the debt begins each day. This is why a loan document has precedence. We can say that a regular Milveh Al Peh has precedence.

Ran: The Rif's opinion is primary. This refers to land. Regarding Metaltelim, there is no precedence. Even if the loan document is earlier, if they come to collect together, they divide the property, for there is no precedence. Therefore, if either collected first, he keeps it.

Poskim

Rema (CM 104:1): If a later creditor comes to collect, we help him collect. When an earlier creditor comes, he can be Toref from the later creditor. This refers to a loan document. If an earlier Milveh Al Peh collected, he keeps it.

SMA (3): The Tur says that when both are Milvos Al Peh, the earlier one collects. The Shulchan Aruch (Sa'if:13) rules that an earlier Milveh Al Peh has precedence even over a loan document, for Shibud mid'Oraisa. Perhaps the Rema agrees; here, he discusses b'Di'eved, when a later creditor collected. L'Chatchilah, he agrees that the earlier creditor collects.

Shulchan Aruch (13): If there is a loan document and an earlier Milveh Al Peh, the Milveh Al Peh has precedence to collect from Bnei Chorin, since witnesses testify that it is earlier.

Bedek ha'Bayis: We follow the Rambam, Rav Hai Gaon and the Rashba.

Darchei Moshe (8): The Mordechai (Shevu'os $) rules like Rav Hai Gaon. The Ge'onim enacted that a lender collects from inherited Metaltelim. Even so, if the borrower was Meshabed Metaltelim Agav (along with) land to Levi in a document, Levi has precedence over an earlier Milveh Al Peh, for Levi's Shibud is letter of the law, whereas the other is only an enactment. This is only if witnesses say that these Metaltelim were around when he acquired the Shibud Agav. If not, the Milveh Al Peh has precedence.

SMA (31): Here, the Darchei Moshe agreed with the Shulchan Aruch! The Tur discusses when the borrower was Meshabed his property to each in front of witnesses. This can also resolve the contradiction in the Rema. All these precedences are for Bnei Chorin land. There is no precedence for Metaltelim, even if one document is earlier.

SMA (31): The Rema holds that Shibud mid'Oraisa, so for Bnei Chorin, we do not distinguish between a loan document and a Milveh Al Peh. The Tur says that the Rif disagrees. The Shibud of a document is like a sale. Just like a Milveh Al Peh cannot collect from a buyer because there is no Kol, he cannot collect from Bnei Chorin that became Meshubad afterwards, because there is no Kol. In Sa'if 1, the Rema wrote that if a later creditor collected before an earlier Milveh Al Peh, he keeps it.