The first time I heard a countertenor was in "The Messiah", he sang the soprano part and I found it not too enjoyable. This was no "hip" wersion; it was a symphony orchestra with a choir of five hundred so why they made this chioce is still a puzzle. I tried closing my eyes and that didn't make any difference, it still didn't sound right. The fact that he looked very much like the late Jim Nabors, a TV personality of the time was no help.
One of my favorite vaocal ensembles is the male a cappella group, Chanticleer. Four alto, four tenors two baritones, two bass singers. I have sen them live many times, have most of their recordings, and put them beside the Tallis Scholars. They did the Palestrina Requiem, dedicated by Palestrina to Pope Gregory. It was the only recording of this music, at least then, and it is far and away my favorite. I have all of the requiems by all the major composers and this brief but brilliant piece just sweeps them away. The first disc by them that I bought is "Sing We Christmas" and with it I lost any interest in a shelf of classical and popular holiday music. It is Christmas to me where the "Festival of Lesons and Carols" used to be "it", no offense to the Kings College Chapel Choir.
To use an a cappella choir for Verdi's Requiem would be insane but for some music, less is more. I have a recording by John Aler which is sublime; he vocalizes "Vocalize" by Rach. with great effect. So, I'd vote in favor of countertenors any day. As long as they achieve their art by non-surgical means!