Scotty's and The RAM. Both are good to us. Give them both a try. Silly to say which one is better. They are both very crowded during Gen Con and their respective staff members work very hard and work long shifts to make our experience a good one. The RAM is right around the corner from the ICC so it;s a shorter walk but Scotty's shouldn't be missed either.
Not so much Gen Con "themed" but also good to us gamers is the local Steak N Shake. They feed us, get us in and out to seat more of us quickly and have always been pleasant to deal with. I spoke to one waitress there two years ago and she said that she was working double shifts (12+ hours per day) there to get money so she could buy things for Christmas for her kids. She also said that many of the wait staff drove in from other cities to help out during Gen Con and that we (Gen Con attendees) are legendary to deal with; always nice, dressed up in costume, lively bunch that tip well and that all of the restaurants in Indy look forward to the Con each year.