I used to live downtown CLE and work in University Circle. The major problem with the eastside property is that you'll be commuting towards downtown just like everyone else, unlike the downtown property, where you'll have the reverse commute with no traffic. The drive from the Marriott East is ~20 minutes (longer if traffic is bad), so if it was me, I'd stay downtown. Situation depending, you could also consider taking the RTA out to University Circle (from downtown) and not have to drive at all (you can take the RTA from the airport so you wouldn't even have to rent a car).

Plus there are some good restaurants downtown within walking distance (Fat Fish Blue comes to mind).

jon