Why did David say "Tzar Li Me'od"?
Rashi: Even the smallest punishment is very harsh.
Famine and a plague are both "b'Yad Hashem." David did not specify which he chooses!
Rashi: Hunger depends on rich people who have stored Peros.
Radak #1: "B'Yad Hashem" hints to a plague, like it says [about Dever in Egypt] "Yad Hashem Hoyah" (Shemos 9:3).
Radak #2: Hunger depends partially on people. They can go to Egypt or other lands to but food. A plague depends only on Hashem.
Why did David choose famine?
Rashi, from Tana d'Vei Eliyahu Rabah 7: He reasoned, if I choose the sword, Yisrael will say that I trust in my Giborim to protect me, and others will die. If I choose hunger, they will say that I trust in my wealth, and others will die. I will choose a plague, which affects everyone equally.
Radak: It would be shameful if Yisrael would be stricken in front of their enemies, or if there was famine and people went to other lands, like it says "v'Lo Eten Eschem Od Cherpas Ra'av ba'Goyim" (Yo'el 2:19).
Radak citing Midrash Shmuel 31:1: He reasoned, if I choose famine, all Yisraelim stricken from hunger will be on the roads. If I choose the sword, all Yisraelim stricken from the sword will be on the roads. Rather, a plague should come.
Radak: Some say that Gad hinted to him "Ashiv Sholchai Davar" - this is like Dever (choose it).
Malbim: Hunger is natural, and the sword depends on human choice. He chose a plague, which is based on Hashgachah; Hashem has great mercy!
