Do you already have a financial aid package from WashU? If not, there's no sense in making the decision now, unless you're pretty sure they're not giving you anything.
That's true, wait untill you see what financial aid you get....I got a full ride at Braindeis but also got into an ivy...and while the ivy's finaid wasn't a full ride, it was a pretty good deal and I graduated without debt. (They had a policy that allows you to cancel out the students' portion with outside scholarships, while--atleast back then--most other schools had a cap where even if you had $10,000 of scholarships, they'd only let you use $2000, and still need to take out $8000 in loans...but I think that's becoming less common).
Also, while it doesn't always work, you can go to the financial aid office, show them the other finaid packages you've received from other schools, and tell them that while you'd love to go to that school, financially you're better off elsewhere, and sometimes they might to make you a new finaid offer. Sometimes the school won't change it, but some do....and if their coach is telling them that they really want you, then they'll probably be able to work a little finaid magic.
All that said, don't pick a school based on name or prestige....pick the school you really feel at home in, and that allows you to do what you *want* to do while you're in college. If you really like Creighton, then go for it, but if you really like WashU, hold on to see what they can do for you in terms of financial aid.