Carnival Journey 14 day Southern cruise this Nov, best port to rent a car?

hi there. My girlfriend and I are doing a 14 Southern Caribbean cruise this November. We can only budget one port to rent a car to do our own thing. Which port from below would be the most advantageous for us to choose as there is the most to see at far edges of the country, so we can do our own thing at our own pace over seven hours that would benefit from a car rental and not a simple excursion? Thanks and any rental recommendations would use be greatly appreciated also.

Antigua, Barbados, Grenada, St Thomas, Tortola and St Lucia.

So are you not doing anything in the other ports? Because if you can only do one thing, I would do Spencer Ambrose in St. Lucia as a shore excursion is the only way to get to see the Pitons up close. This was one of the best shore excursions we have ever done.

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