October is a great time to visit the parks. The weather is more pleasant than May and the crowds for SeaWorld and Busch Gardens are lower In October than May. If you plan on going to SeaWorld or Busch Gardens on the weekend in October, you'll have busier crowds than the weekdays but no where near what you'd find at Disney. Weekends in October, SeaWorld hosts their Halloween Spootakular which has a focus on younger kids. Unlike Disney's Halloween event, this event is included with park admission. Starting at noon, you will have free trick or treating and fun shows featuring characters like those from Sesame street. So if you have younger kids, this is a great event for them. Busch Gardens also has an event on Fridays, Saturdays and Sundays at night. It's called Howl O Scream. Howl o Scream is not included with park admission and is a separate ticket from a regular day ticket. Howl o Scream is definitely for an older crowd, like teenagers and adults. There are haunted houses to go through, sections of the park also become "Scare Zones" where there are plenty of frights and most of the rides are open too. I think Howl O Scream is worth the extra ticket. It usually runs around $40-$50 per person. I always make sure to go a few times in October because I enjoy it so much.
Like I said, October is better weather wise for your Discovery Cove trip. It wont be as hot but it wont be cold. It will be comfortable. In May, you run the high risk of daily thunderstorms that will interrupt your day. The rainy season is usually over by October so you don't have to worry about thunderstorms.
So if I were you, I'd definitely visit in October. You have a lot more extra options to choose from and much better weather. Crowds are also better in October. Hope you have fun!