The best park to visit today is Magic Kingdom. You should also be ok to visit either Hollywood Studios or Typhoon Lagoon as we expect average crowd levels there. You should probably try to avoid Epcot or Blizzard Beach or as we're expecting a fair few people to visit there.
There aren't any morning Extra Magic Hours planned at any park today.There aren't any evening Extra Magic Hours planned at any park today.
If you don't plan on watching evening fireworks or other events during the day, try and visit the most popular and busy attractions when said events are on. Since a large number of the parks visitors will be at the event, you should find the rides are fairly quiet.