Both but tickets for postal and crown are separate and sell out quick, must reserve in advance. We used https://www.smartdestinations.com.
Its better to buy in advance to avoid hassles like queue, non availability etc.
You can buy in the day of. It s easy to buy, but you must arrive earlier or you will wait a lot of time.
If you mean the boat to the statue, the day of is fine. Ferry leaves every 20 minutes. As for tickets to get up, they didn't seem hard to get day of.
Buy it online .you can find good deals on Groupon.
It solds out too quick. But it online specially if you want to climb until the crown
It's better to buy it online. There are many people trying to buy it in peron
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