Tables or Stadium seating for a conference?
Since it's a one-day conference, I'm assuming it's a little more relaxed than a powerhouse 3-day affair. But even then, I think the classroom format is a little more appropriate. Here's what happens with the table format:


either people will have to move chairs around to see the speaker, in which case you've effectively created a classroom format with much less desk space. 
or people start talking to each other and ignoring the speaker. I've seen this happen in particular at business meetings, where arguably it's less important to listen closely, but the level of noise created is still annoying. 


Either way, it's not serving its purpose. By all means use the table format for the coffee area or break spots. But I don't think it makes sense for the conference itself.