Merthyr Tydfil
If you mean condition-wise, the board is a priority to check. System 1 hardware even at the time was known for not being well-designed.
If you mean gameplay, most System 1s play like one step above 70s EMs - no bad thing in itself. You won't find much with ball-to-ball memory though, and the majority are about maxing the bonus (generally 20,000 and up to 5x), collecting it from a lit eject pocket, and repeating. What you will get are drop targets, rotos and / or varis, and more interesting layouts than Bally were doing at the time. If you like rotos, look for Close Encounters or Torch. If you like drop targets, then Joker Poker or Count-Down are the games for you.
