I personally recommend the green mango shake, with milk and syrup. (It tastes horrible without both.)
Frankly I find the green mango shake at Lutong Bahay in Area 2 better. I think they added copious amounts of sugar to it instead of milk and syrup. The result is a concoction both sour and sweet that tickles your cheeks.
Lutong Bahay apparently took green mango off their list of choices sometime during the summer term, though, which is quite sad. Maybe someone should start an online petition.