CAUTION: NOT A TEACHER
(1) You are a very intelligent person. Yes, one must be very careful about what one
reads on the Web. And, yes, you can depend on the answers here that you get
from the teachers.
(2) I found something from an American expert named Bryan A. Garner. One of his
books is A Dictionary of Modern American Usage. Many people seem to think that
he gives accurate advice.
(a) He writes that
(i) The words are "equally good."
(ii) "Euphony should govern the choice."
(a) My dictionary tells me that "euphony" means "pleasing to the ear."
(i) I guess that he means that you should consider all the words in the sentence and then decide which word ("someone" or "somebody") sounds the most pleasing to the ear when it is used with all the words in the sentence. Of course, this is a difficult decision for us ordinary native speakers. So it would be really difficult for a learner.
(b) Mr. Garner says that (in his opinion) the word someone is "often better" if you are
looking for euphony.
(c) I know nothing (nothing) about the rules of pronunciation. But which word do you
think sounds "more pleasing" to the ear, and which one is easier for you to
pronounce? Say the word "someone" out loud; then do the same with "somebody."
As for me, I feel that the "smoother-sounding" word and the more easily pronounced
word is someone.