However for people of yeshiva ages it is best to be in an authentic Lithuanian yeshiva during the year. And it is my impression that it takes a special kind of human being to be a real Rosh Yeshiva. I knew a few of the authentic types--like Reb Shmuel Berenbaum and the other teachers at the Mir in NY. [Avraham Kalmonovitch, and the author of the Sukat David--I forgot his name, But I really liked his book on Ketubot. ]But these types are rare. If you have met, the real thing you can't be fooled anymore.
It is like the storyabout a merchant that had a servant. He was on a trip and came to an inn and they served to him what they claimed was Hungarian wine--the rarest and best. The servant told the master, "This is not Hungarian wine."
"How do you know?" he asked.
"Because I was in Hungary and tasted the real thing. Once you have tasted the real thing you can never forget it. And this is not the real thing."
I say also one you have seen and sat in a class of an authentic Rosh yeshiva, you cant be fooled anymore.