It will be much harder for both if say the laundering medium used is fiat. It's harder for the law enforcement since fiat isn't traceable unless a big amount of money suddenly enters into the account of someone that doesn't have any kind of that bank activity, and it's hard for the launderers since you can't easily inject the money in a business or someone's bank account, it needs to look normal and at the same time efficient. It's a good thing that drug dealers and launderers use bitcoin because it's much easy for the cyber police to track them down via the public ledger, if it was XMR or other privacy coins, it's.going to be a win for the launderers.