Looking at the two different itineraries:
The Explorer of the Seas departing from Miami is doing alternating 7 day Eastern and Western Caribbean cruises, visiting Belize, Costa Maya Mex, Cozumel Mex, and Grand Cayman on the Western (4 ports), and San Juan PR
, St. Maarten Netherlands Antilles, St. Thomas USVI, and Nassau Bahamas on the Eastern (5 ports).
The Norwegain Spirit departing from New York City is doing 10 and 11 day Eastern Caribbean cruises, visiting St. Thomas USVI, Antigua, Barbados, Grenada, Dominica and Tortola UKVI on the 11 day cruise (6 ports), and St. Thomas USVI, St. John USVI, Barbados, St. Maarten Netherlands Antilles, and Tortola UKVI on the 10 day cruise (5 ports).
The Explorer of the Seas is the larger ship, at 142,000 GRT, in comparison to the Spirit, at 76,800 GRT. It's approximately twice the size and it will have approximately twice as many passengers.
But if you want a longer cruise, the Spirit accomplishes that well. By November, the first day out and the last day in to NYC, it will be too cool for anyone to be using the swimming pools aboard the Spirit.
The itineraries are sufficently different that makes a ship to ship comparison hard. Which itinerary do you like better?