I really like the feel of the MD-88/90 up front. It's quiet, with the engines in the back, which would be the same for the B717. OTOH, since the B717s are new, and I haven't been on one yet, that would be a cool thing for me, as a semi airplane buff.

That said, MDW is substantially closer to downtown Chicago, if that's where you're headed. If you're taking the CTA train in, the train ride is a little bit longer from ORD (& $5 compared to $2.25 from MDW). Although I've never used a taxi or limo there, I'd certainly think that I'd rather use MDW, as I have seen some NASTY traffic on I-90 riding in from ORD on the Blue Line.