Roth gives you the most flexibility down the road and is the best long-term plan if you don't end up using the money towards a house. If this would be your first home purchase, you are allowed to take up to 10k (or something like that) from your Roth to put towards your house's down payment. You'll probably have to pay taxes on the gain, but if the money goes towards a first house purchase, you don't have to pay the 10% penalty.

ETF also gives you flexibility and you can use it towards the down payment on a house.

529s is the least flexible, and your house and retirement should come first over your kids school.