I did a bit of research using raw data collected through AI's systems and other sources and it appears that AI 136 LAX-FRA-BOM/DEL is the most delayed flight in the system with a shocking 98.5% irregular operation or delays since May (note that these statistics are unofficial and due to non-standard sources of the raw data may not be entirely accurate).

The best longhaul flight in the system for 2005 is AI 130 LHR-BOM (formerly AI 160) which operates in excess of 90% on-time (using a mixture of 744/772/343 equipment).