Wait till the third map pack is released and see what the community feedback is for it. Then you can get a sense of how all the maps in each of the three map packs plays and their size. Based on that info, then you can decide whether you want to purchase the packs individually or get the map pass for all 3.
The first map pack focused on big team battles. The second is more 4v4 maps. The third seems to be a mix, but we'll see what happens.