If I were to pick a favorite classic stern, it's Galaxy, because it was one of my three first machines and I really did enjoy it.
For Bally, it's both Strikes & Spares, my very first pin, or Dungeons & Dragons, which I played for hundreds of hours on break times at my first summer job.
I have neither machine at the moment, but am amassing parts to get a Strikes & Spares and do a full restore on it. Already have a NOS pf from Kruzman, and plastics from CPR.