I've seen a lot of different wargaming styles and most of them seem to boil down to two basic types in most cases. I'll call them the killer stack method and defense in depth for lack of better terms.
I would define the killer stack method as a style where the defending player seeks to build a very strong line of interlocking defenses with almost everything he has forward deployed. Large machine guns, ordinance and even vehicles might be integrated right into this network. This kind of defense can indeed be strong, but it can also prove brittle if hit in the right way. The obvious advantage is that the defender stands less chance of being defeated "in detail" while the attacker picks off his units one at a time. Instead, the defender is able to concentrate his firepower for maximum effect right from the beginning. Attackers will likely attempt to penetrate such a defense as quickly as possible and thus minimize the amount of time spent in exposed positions.
The disadvantages of the killer stack method are also clear. If the defense can be decisively penetrated at any point the entire line might prove untenable and force a general withdraw. Should this occur there will likely be a short time where a significant portion of the defender’s units are somewhat disorganized and exposed while they attempt to redeploy into fall-back positions. An attacker who hits the line with enough force to affect a penetration and then aggressively exploits this penetration has a good chance of inflicting so many casualties that the battle will be won.
The other kind of defense is what is generally referred to as defense in depth. This defense is built around the concept that artillery and long range weapons systems are always the greatest threat and always pose the greatest risk of inflicting mass casualties. Large concentrations of troops are to be avoided as these simply create target-rich environments and make the attacker’s job easier. Instead, the defender carefully constructs a layered defense using interlocking fields of fire and kill zones. Terrain will have a major influence on how such a defense will be implemented as will the number and type of troops available. Although some strong points might be integrated into a defense in depth in order to safeguard key terrain, the bulk of the force would not be lumped together. The advantage of this method is that artillery and other long range weapons will be far less effective. It may also be difficult to overcome single defensive points by using smoke because each point is protected by mutually supporting positions. Because the defense has depth to it, this can work to give the defender a small amount of time to reposition forces deployed to the rear should that become necessary during the course of the battle without disrupting the entire line.
This method also has disadvantages. Because the defense is somewhat more dispersed it may not be possible to inflict as many casualties on the attacker. Also, there is a risk of units being defeated in detail should the attacker make effective use of smoke, fog or darkness (but that is always a risk to some degree no matter how the defense is setup).
There are other types of defenses as well and I’m oversimplifying this a great deal in order to make the distinction clear. A mobile defense can prove to be the strongest in a lot of situations, but this type of defense is highly dependant of the type of equipment available, logistics and the weather. This is also a much more complex form of defense and takes more skill to pull off.
How do you generally tend to play when on defense? Are you an everything up-front man, or do you prefer depth?
Likewise, a fixed defence is asking for a treatment of artillery.