When I use mango I cut it up into smaller chunks. The idea being more surface area comes in contact with the beer. That said, my experience with mango is that it is a delicate fruit, lending minor notes to the beer. If you are going to dry hop a beer and/or have big flavor/aroma additions of hops, the mangos will definitely be over powered if not nonexistent.
I just finished up a Mango and strawberry Weizen.. I diced everything up fine, and added it to the wort at about 180 degrees. I let it sit for 20 minutes before chilling. I left everything in the primary for 2 1/2 weeks, and then bottled. I smell strawberry, and taste mango. But, the beer is still young.