Lakewood has much more Torah, space and cheaper housing.
Flatbush has a larger variety of kehilos and Yeshivas. e.g. There are more Mesivotas in Lakewood but if you want a good one that also offers a good secular education you will have a easier time finding one in Flatbush. If you want a shul with a Rov that you can build a relationship with you also will probably have a easier time in Flatbush.