You will have to define "best" when it comes to both airlines and airports. My definition may not be the same as yours or someone else's.
The best airport (to me) is the one closest to me that gets me where I want to go with the minimum number of connections and in the least amount of time. But I won't spend hours and hours driving to get to an airport just to save an hour or two flight time. YMMV.
I use Google Flights to search available flights from my home airport. You could also check flights out of any other international airports closest to you. In your case, I believe you flew out of Orlando last month. You could also check flights from Miami if you are willing to drive that far to catch a flight. Google flights will show the airline, price, flight duration, any connections, and the connection time. You can use filters to narrow down the possibilities. For example, you can restrict selections to non stop flights, which will give you only 1 flight a day from Orlando, but at twice the price of flights with a single connection. Your choice.
As far as the best place to purchase flights - that would ONLY ever be directly with the airline, unless the flight was included as part of a package vacation.