Q. What is the correct pronunciation on the goimel brocho, kol toiv or kol tuv. Most people say tuv, but in sidurim it says toiv?

A. Horav Shlomo Miller Shlit”a stated that the sidurim are correct and “toiv” is the right pronunciation.

Dikduk teaches that when the noun Toiv becomes an adjective (shem toar) and qualifies or modifies a noun, it will change to Tuv, for example: “Tuv Eretz Mitzraim” (Bereshis 45: 18) etc., by itself it is read Toiv.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a