Gemara

R. Avahu: We bless on the rain from when the Chasan goes to meet the Kalah

Question: Which Berachah do we say?

Answer (R. Yehudah citing Rav): 'We thank you, Hash-m Elokeinu, for each drop that You cause to descend.'

R. Yochanan: We conclude 'If our mouths were as full of song... Baruch Rov ha'Hoda'os.'

Objection: Are only most thanks due to Him, and not all?!

Correction (Rava): Rather, we say 'ha'Kel ha'Hoda'os'.

Rav Papa: Therefore we say both, Rov ha'Hoda'os and ha'Kel ha'Hoda'os.

Berachos 59b - Mishnah: On rain (one blesses ha'Tov veha'Metiv).

Question: We say a different blessing!

R. Avahu: We bless on rain when the Chasan goes to meet the Kalah

Rav Yehudah: We bless 'We thank You for every drop...'

Answer #1: If one hears that rain fell, he blesses ha'Tov veha'Metiv. If he saw it, he blesses 'We thank You for every drop...'

Objection: Hearing about rain is good tidings. The Mishnah also taught good tidings (surely, rain is a different case)!

Answer #2: In both cases, he saw it. If much rain fell, he blesses ha'Tov veha'Metiv. If only a little fell, he says 'We thank You....'

Answer #3: In both cases, much rain fell. If he owns land he blesses ha'Tov veha'Metiv (Hash-m did good to him). If not, he blesses 'We thank You....'

Rishonim

The Rif and Rosh (1:3) bring the Gemara verbatim.

Rif (Berachos 43b): One blesses ha'Tov veha'Metiv on rain only if he owns land and has a partner. If he owns land by himself, he blesses Shehecheyanu. The general rule is, one blesses Shehecheyanu on something that benefits himself, and ha'Tov veha'Metiv on something that benefits himself and others. If he does not own land he blesses 'We thank You for every drop...'.

Rebuttal (Rosh 9:15): He does not need a partner to bless ha'Tov veha'Metiv. It suffices that the tidings benefit others. One blesses ha'Tov veha'Metiv on an inheritance if others also inherit, even if the Mes already specified that each heir will receive something by himself. Rain benefits also one's neighbors!

Defense (Magen Avraham OC 175:4): The Rif holds that ha'Tov veha'Metiv applies only when the people are partners in the benefit. It does not suffice that others benefit.

Rif: He closes Rov ha'Hoda'os veha'Kel ha'Hoda'os.

Rebuttal (Ba'al ha'Ma'or): I heard that Rav Papa concludes that we say both, i.e. 'We thank You for every drop...', like Rav, and 'If our mouths were full of song...' like R. Yochanan, but the closing is 'Baruch Kel ha'Hoda'os.' The Rif understands that Rav Papa teaches how we close the Berachah, i.e. Rov ha'Hoda'os veha'Kel ha'Hoda'os. This is unreasonable.

Defense (Milchamos Hash-m): R. Yochanan adds to what Rav says. If Rav Papa teaches that we say both, this is totally like R. Yochanan. Rav Papa would not have said 'Therefore, we say both'! Rather, he teaches that we also say Rov ha'Hoda'os, which connotes Ribuy (the great amount of thanks due to Hash-m). However, it can also connote most, but not all. By also saying ha'Kel ha'Hoda'os we show that here Rov only connotes Ribuy. A minority of texts say 'Baruch Kel Rov ha'Hoda'os'. This is correct.

Rambam (Hilchos Berachos 10:5): If much rain fell and one owns land (himself), he blesses Shehecheyanu. If he is a partner in the land, he blesses ha'Tov veha'Metiv. If he does not own land he blesses 'We thank You for every drop...Baruch Atah Hash-m Kel Rov ha'Hoda'os veha'Tishbachos'.

Question (Beis Yosef OC 221 DH u'Mah): I do not understand why he adds 'veha'Tishbachos'.

Rambam (6): One blesses this if there is so much rain that puddles go to greet each other.

Hagahos Maimoniyos (4): Some say that it is when a drop falls and a drop on the ground rises to greet it (Rashi and Rosh). Others say that it is when streams of water descending from the markets meet each other.

Poskim

Shulchan Aruch (OC 221:1): If people were troubled due to lack of rain, and rain came, they bless even if it is less than a seasonal rainfall.

Bi'ur Halachah (DH Im): The Rambam did not say that the Berachah is only when people were troubled, but presumably he agrees. Normally, he only writes what is explicit in the Gemara. In Eretz Yisrael, people are normally anxious for the rain. If this was not the case, it is not clear whether or not one should bless. In Eretz Yisrael one should bless, but without Shem and Malchus.

Kaf ha'Chayim (1): Most do not distinguish Eretz Yisrael from other lands. One blesses only if rain was withheld.

Shulchan Aruch (ibid.): There must be enough for puddles to go to greet each other.

Rema: We are not accustomed to say this Berachah nowadays because our lands generally have enough rain, and rain is not withheld so much.

Beis Yosef (DH Kosav SMaK): Even in such places, if rain was withheld one blesses when it comes.

Shulchan Aruch (2): If one does not own land he blesses 'We thank You for every drop...Baruch Atah Hash-m Kel Rov ha'Hoda'os.'

R. Mano'ach: The text mentions salvation from the sword because when there is hunger, bandits plunder and kill.

Shulchan Aruch (ibid.): If he one owns land with a partner, he blesses ha'Tov veha'Metiv.

Magen Avraham (2): A Nochri partner does not count, for their benefit is not good.

Shulchan Aruch (ibid.): If he owns land himself, he blesses Shehecheyanu.

Magen Avraham (1): The Shach says that if one has a family he blesses ha'Tov veha'Metiv. This is wrong, for the Gemara needed to say that he is a partner in the field to justify ha'Tov veha'Metiv. This is unlike the birth of a boy, in which his wife is a partner (part came from her), but a man need not share his field's produce with his family.

Mishnah Berurah (4): We follow the Shach, for many Acharonim agree with him.

Kaf ha'Chayim (12): It is not clear whether or not Shehecheyanu and ha'Tov veha'Metiv apply even if rain was not withheld.

Rema: Some say that if one heard that rain fell he blesses ha'Tov veha'Metiv.

Question (Magen Avraham 2): This is obvious. It is the same as seeing rain. Why did the Rema need to say it, and why does he say that (only) some say so?

Answer (Magen Avraham 2): Perhaps the Rema saw only what the Beis Yosef cites from the Rashba, and thought that even one without land blesses. However, it is clear from the Rashba that this is not so.

Mishnah Berurah (7): The Shitah Mekubetzes does not distinguish between seeing and hearing. However, others say that 'We thank You...' was enacted only for seeing, and one who does not own land does not bless at all for hearing. We are lenient about Safek Berachos.