Basically, the comments above are not quite fair and not precise.
SQ has the best user UI and linkage to Cadence Allegro layout tools and also provides lots advanced usage if you know how to use its byproduct numerical RLCG results. However, SQ main problems IBIS 3.2 support issues and unable to simulate cross split plane problems.
ICX has the best supports to IBIS 3.2 and also well integration with mentor layout tools. But it is notvery good as a general simulation tool for most major layout tools as it claims for. There are too many geometry data loss during cross-layout format translations. The latest ICX also provides advanced simulation engine for mixed Spice-IBIS simulation. Its new MoM simulation engine provides more accurate results with reasonable simulation speed. But ICX still can't simulate cross split plane problem !?
HyperLynx 7.0 provides better integration improvement with ePD and linesim to boardsim. It also adds liong-waiting lossy TL simulation capability and via L&C parasitic simulation. However, HyperLynx 7.0 has the slowest simulation speed and still can't handle cross split plane problems. HyperLynx 7.0 provides better stimulus train definition and eye pattern data stream. The cross layout tools support quality is still unkown for now. It has good IBIS 3.2 support as ICX. In general, HyperLynx 7.0 just adds missing simulation accuracy and has great improvement in user interface compared previous version.