I second JeanMi, fruit or syrup will work. Traditionally the Belgian brewers would add the cherries to the fermented beer then leave it in the conditioning tanks for 12 months as the cherries get eaten away by the yeast leaving only the stones. There are not many breweries left doing this but the results are spectacular.
Most of use now use fruit syrups, or fruit run through the blender. I often freeze my fruit to burst the cell walls and extract the flavours more rapidly.
Again as JeanMi rightly worries, you will end up with fermented cherry flavour, but to my mind that is a wonderful thing.
I am not sure we can precisely answer your question as 'Best' is very subjective. Most traditional is to add whole cherries and wait, most rapid is to take a blender and make a cherry syrup. It totally depends if you desire speed or are a sucker of historical methods.