I like interior funneling better, just because if it is used correctly, it can be the most deadly thing in the game, but I use exterior funneling because it is easier to incorporate into bases.
For exterior funneling, I like to use either a bomb and a spring trap or 2 spring traps. The attacker might think that there is only 1 trap, so he/she will send in 1 giant followed by 12 more. 4 fly and they only have 9 left which is just not enough to take on a base with a giant heavy army.
For interior funneling, I like to use staggered buildings and leave a gap open so it is guaranteed that giants or infantry will fly up if they choose to go that way.





