what is wrong with the posters here? there is no such thing as a bad language. every language that you learn is good. yiddish is good. ivrit is good. hebrew is good. man alive.
as for the “jewishness” of each language, it all depends on what factors you use to determine jewishness of a language. both have many non-semetic words as part of their vocabulary but yiddish is mostly non-jewish words while ivrit is mostly jewish words. in fact, there are probably more “jewish” words in other semitic languages such as arabic than in yiddish. that being said, yiddish is only spoken by jews so it gets some points for jewishness for that. but then again, so is ivrit.