Okay I have an endless amount of recommendations.
First off do they want completed manga? Ongoing manga? Are they okay with slightly older manga?
For everyone my recommendations are usually
Fairy Tail
Naruto
Witchcraft Works
Full metal Alchemist
Pandora Hearts
Owari No seraph (Seraph of the end)
so...so...so many more.
Some good "boyish" manga (I say that because I am a firm believer than girls can like shounen and boys can also like shoujo) would be things like Kuroki no Basket, Slam Dunk, Yu Yu hakusho, Kenichi: History's strongest deciple, One piece, Code Breakers.
Shoujo manga that are good are Fruits Basket, Vampire Knight, Tu love ru and ouran High school. But there are an endless amount of manga in all genre's that are really good.