Also wondering what is the best/easiest way to get to either?
Where are you starting from?
If you fly to Belize City, you can get to AC on a domestic flight (maybe 15 minutes, Tropic Air or Maya Island Air), or by water taxi (an hour or so, but a lot cheaper). You can get to Corozal by domestic flight, or by road (rental car, bus, taxi, transfer service).
If you fly to Cancun (might be cheaper), you can get a flight to Belize City (Tropic Air), or an ADO express bus to Chetumal (Mexico) where you can continue to AC by water taxi (daily service), or continue to Corozal by road (bus, taxi, transfer service).
You've asked for best & easiest, so I say that would be any option that includes flying or transfer service (where possible).
More details of transportation options here...http://belizebus.wordpress.com/