I'm Lucy, and I'd be happy to answer your questions today.
In either New York or Florida, a prenuptial agreement is typically valid as long as the parties are over the age of 18, mentally competent to enter a contract, and are not under duress or being forced to sign the agreement. Florida law requires that spouses disclose all their assets before entering a prenuptial agreement or receive a written waiver; New York requires only that a person does not misrepresent their financial situation. Under Florida law, if a prenuptial agreement waives alimony BUT the spouse would have to apply for public assistance without it, the judge has discretion to still enter support (that's going to be more important if the spouses divorce in Florida than if they sign the agreement there).
New York will not enforce an unconscionable agreement, meaning one that so seriously favors one party over the other that the judge cannot enforce it. Florida will not enforce an unconscionable agreement only if the party who signed it wasn't aware of the other spouse's financial condition at the time of signing. But you should also know that, in any state, a judge can refuse to enforce an agreement if it would violate the public policy of the state. So, again, where the parties divorce (if they do) can ultimately be more important than where it's originally entered.
It is a good idea in either state to have the agreement signed in front of a notary so neither spouse can later claim that he or she did not sign it. If you're planning to enter a fair, balanced agreement where each spouse has fully disclosed all assets to the others before it's signed, it should not make much difference whether it's entered in Florida or New York.
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