Yes, I would definitely just keep it liquid. The best way to buy a house is to be ready with your down payment and able to jump on a great deal the second you see it - so if you have your money in an index fund and it takes a dip, you might not be able to put down the down payment you want. And I would definitely say that being able to put down 20% on a house and not have to pay PMI, ever, is a guaranteed return on your money whereas you may or may not make any money putting it in an index fund!