Taxi is a fantastic game. Only reason I let mine go is because I traded it for Mousin'. I never really cared for Earthshaker. It just felt like the player was beat over the head with the theme and the gameplay and limited jackpot collect got old after a couple games.
Whirlwind is the best system 11 game but it's not really because it stands on it's own as the best, it's more because of what it's ruleset evolved into with later releases like Funhouse and Addams. It's like saying High Speed is better than Firepower. Of course it is! No one cares that it's a "system 6" and High Speed is the first "system 11", completely rewriting and understanding what it takes to design a good pinball, moving forward. Whatever came after that machine had to top the next one in a way that required a huge step forward in thinking.
I mean, if you want the honest truth, Whirlwind is the overall best game up to that point in time in the entire history of pinball. Is that what you should buy? Probably not because it may not make you a happy pinball owner and, using that thinking, you should just buy Funhouse, or AFMr for that matter.