Clash of Clans – Best Defensive Barracks Troops

Defense is pretty important in Clash of Clans. If your defense was somehow impenetrable, and you were infinitely patient, you could technically acquire all the resources you need for upgrades just by waiting and tapping your collectors occasionally.

However, no defense is perfectly impenetrable. Someone who spends a lot of time or money on the game can bypass virtually any defense. They're coming, and they'll take your resources. Also, very few people are infinitely patient.

Thus, raiding is the way most people get most of their resources, so offensive capability should not be neglected.

All that said, there's no reason to neglect either of them. Most defensive buildings require gold, while most offensive buildings and units require some type of elixir. Builders can be somewhat scarce, but honestly you should be prioritizing both of them in order to get ahead.

Most units that do not have any favourite target, such as barbarians and archers, go after the closest unit/target. However, units that have specific favourite targets, such as giants and balloons, go after their favourite target before moving onto the rest of the village when all the favourite targets are down.
However, it is useful to note that ground troops are affected by the precense of walls. Melee ground units would normally destroy everything outside the walls before attacking the walls themselves, unless there is an opening in the walls. However, ranged ground units are not affected by walls unless their targets that are hidden behind walls are outside their range of attack. If their targets are out of range, then they will just ignore the target and move on to the next nearest reachable target in the surrounding area.
Air units will not be affected by walls as they can always fly above them.
With Giants and Goblins, it gets a little more complicated, we should all know that after spawning units go after their nearest favorite target. Once that building is dead, they then go after the next nearest of their favorite target. But what happens if the nearest favorite is behind a wall? Well then the units need to decide which to go after. This is dependent on distance and how hard the closest target is to get to. The units will prefer to go after the close one, even if it has to kill a wall first, if the father target is more than roughly 15-20 steps away. Both Goblins and Giants operate exactly the same, except for their target. Balloons operate nearly the same way except for the fact that they are not affected by walls.
Healers are unique in the sense that they heal instead of damage. Once they locked on to the nearest injured ally, they will not stop healing him/her until either he/she is dead or fully healed. After that, they will go to the next nearest injured ally, regardless of what threats there are, so naturally air defences are a killing blow to them. They also have AOE effect of twice that of a wizard tower and half that of a mortar.
For wall breakers, they attack the nearest wall. Additional wall breakers placed after nearest wall is destroyed continue in a straight line past the destroyed wall, allowing detailed aiming at inner walls of bases. Here is a table showing how many wall breakers (of a given level, y axis) it takes to destroy a wall (of another given level, x axis)


Hope this helped :)

Adapted from: http://clashofclans.wikia.com/wiki/Flammy%27s_Strategy_Guides/Unit_Strengths,_AI,_and_Pathfinding_Guide
(For more deatailed information, you may want to visit the above mentioned website.)