Actually, the more I think about this, the most liquid charizard is the charizard card that you own that you like the least.
For collectors, the biggest hurdle is that you don’t want to part with the cards that you own, not the price (unless you have financial hardship).
It doesn’t matter how easy you can sell a 1st base charizard when you don’t want to part with your card. On the other hand, if it’s any charizard you don’t feel like it’ll compliment your collection, cutting the price and selling it cheaper to quickly get rid of it guarantees to be the most liquid strategy.