We take daugther to AG a couple of times a year. Depends on if you also would like a pool. The Westin North Michigan is quite convienent but no pool.
Inter-Contential not very convienent to AG but probably half between AG and Navy Pier if doing this and Children's museum (recommend)at NP - pool former olympic training pool, but small and no shallow end.
Also close w/pools Hyatt, Omni and Doubletree.

another hint - if you plan on having tea or dinner at AG book early! Sunday brunch usually not a problem but Tea and dinner fill up early.