The information that is posted above is mostly inaccurate, but, the request is so subjective that answering is virtually impossible. Yeshivish and not too serious are generally a contradiction so it really depends on what hthe OP means by each. I will give it a try though. How about Rabbi Rabanowitz in Washington Heights or Rabbi Avrohom Shulman in Elizabeth? Rabbi Alster in Cliffwood? Rabbi Pikis in Engelwood. Rabbi Frankel in Monsey? Rabbi Sender in Monsey? Rabbi Zoberman (new) in Monsey? There is somewhat of a range here, but all within some loose boundries.
Or better yet, call Rabbi Binyomin Strauss in Lakewood. Places more bochurim than anyone else in the world