I would recommend using neither as the limit for either is 10k entries, which means 10k blocks. To save structures ideally I would use lists of texts that have been given a compressed string that contains the block data. The limit for texts is 2k characters so you could assign every used block a value in a dictionary at index 1 of the list so every block is some number of characters. You could also preset certain symbols for common blocks such as air, or have single digit codes set aside for the most common block that will not be used elsewhere so air takes up less space. You could also use certain symbols to represent amounts of air (Such as a period is one, comma is two, etc.). You should also set the size of the structure in this dictionary with some other name, only lowering the limit of unique blocks by one. On top of this, to store nbt data and container contents, you would need another dictionary set aside for just that. The key could be the coordinates and you could set the block data and such in the value. Im not the best dev so there are prob better options but this is the one I would personally use
