I've never actually stayed at either, but do stay in that area a lot so have seen both hotels and would tell you that the Renaissance is nothing special and I wouldn't pay much more for it compared to the Marriott.

If you're not married to the Marriott chain, the Hilton Suites Oak Brook would be a much better choice in my opinion, especially for a four night stay, it's about a 1/2 mile from the Renaissance and a mile from the Marriott.