I went to SCI a couple of times in Reno. IMO, the level of "blue bloodedness" and "my schittt don't stink" attitude at SCI made me never desire to go back. DSC is a much more friendly, laid back atmosphere.
This for starters. IT is also Wayyy less expensive to get in and see the exhibits and the fact it's earlier, one tends to have a better opportunity to book. Also, check with the exhibitors off the record and ask them as well..