CAhobbit
Super Freak
The panels are very hard to predict. Some are easy to get into and some are surprisingly hard. I was actually shocked by the line for Sideshow's last time. The guards kept saying we wouldn't get in, but we did. Go figure. Hall H is HUGE! I haven't had a hard time getting a seat though, but they are usually in the back, which is fine because of the screens. Most of the time I'm just happy to be in the room.
I've had many occasions where I couldn't get into a panel (and it's either been with hall H or ballroom 20). Because of the problems I've had in the past I always go at least 30 minutes or more ahead of time for a panel.
I do remember the year they did a Bruce Campbell panel in a room that held only 100 people. Yeah, that was smart. The line of people hoping to get in was HUGE and I never did get into it.
It's true they are hard to gauge but I already know the ones that will always have a big draw are...WB panel, Kevin Smith, Futurama, Joss Whedon and any highly buzzed movie.