After playing or GMing everything the following RPGs had to offer in their day, I would gladly do it again: d6 Star Wars, James Bond 007, and Spycraft.
For any group to have a great 2 hour session it would be best with which ever system they are most familiar. That makes jumping into an investigative/puzzle solving session, a role playing session, or a combat oriented session a great success. For my current group it would be D&D 5E.