Do the Math During Preparation Day
When scouting a base during Preparation Day, you can see the levels (and effective target area) of the defensive objects. Using the damage information posted at (http://clashofclans.wikia.com/wiki/Defensive_Buildings), you can add up the total ground damage and the total air damage for a specific base. If you find a base has very strong air damage relative to it's ground damage, a ground based attack is your best offense. Don't forget to assume max number and level of hidden traps for the Town Hall level of the base you are scouting.