Some time ago, earlier this year, I had the opportunity to attend to a conference where one of the leading SIM vendors (according to gartner's magic quadrant at least) talked about their product. Although my opinion will always be biased and I tend to compare all that I see on this area with OSSIM, I also believe that I've got a solid base to judge others.
Anyway, since I know myself and making a review comparing more than five years of work with a 5 hour demo and some document browsing isn't fair, I won't say the name of this product.