For the four systems I bought (Labyrinth Lord, Basic Fantasy, ACKS, and DCC), Goodman games DCC is hands down my favorite to run. The character generation funnel system, warrior mighty deeds die, the disfavor system for clerics - corruption for wizards, and random spell results for all casters, all come together to really make the system shine, and still deliver a very old school feel. I ran a sand box style campaign for a time and really enjoyed the flexibility of system.