My personal experience shows that quick cannons offer the most potential for damage to a single target. The greatest disadvantage of quick cannons is their limited range, but this can be made up for with proper placement. An asymmetrical design is required for high scores with the quick cannon. With their limited range, 30% of your quick cannons will be unable to do significant damage to the ant before it reaches the goal if placed evenly around the hill. Watching patterns in the ants' movement you'll notice that they tend to avoid the center, and more importantly, they tend to stick to the top of the screen. Placing most of your cannons to the right of the ant hill will give the ants the most resistance. This strategy may cause the ants to favor approaching the ant hill from the bottom, but this can be avoided. Here is the best quick cannon strategy I've found:
1. Creating three quick cannons initially has shown me the most success. One is placed exactly diagonal from the top left corner of the screen. Two more are placed along this line. (Screen Capture: http://www.billmanolios.com/forfun/antbuster1.jpg" ). The two red cannons are impact cannons. These will eventually become ice cannons, but for now the extra damage is more important than the slowing effect. The order in which these cannons are upgraded is determined by the ants' preferred egress route. For example, if the ants are choosing to go right, upgrade that cannon. At this point the ants will not have a strong preference as to which path they take and will change their minds often. Place your strongest cannons on the ants' preferred path (most likely the right) but keep extra money on hand to upgrade your cannons on the other side if needed.
2. At level 40 the ants will begin to reach the cake easily. This is the time to upgrade one of your impact cannons into an ice cannon. Again, upgrade the one that is likely to be the most effective. (Screen Capture: http://www.billmanolios.com/forfun/antbuster2.jpg ). Continue to build more quick cannons as you earn more money but keep $400 reserved for creating your second ice cannon.
3. Around level 70 it'll be time to upgrade those ice cannons fully. With this strategy you can do well with only two ice cannons on screen, saving more money for quick cannons. (Screen Capture: http://www.billmanolios.com/forfun/antbuster3.jpg ). Meanwhile, the quick cannons continue to grow heavier on the right side. Every once in a while you'll be overwhelmed by the ants as they bring in three or more pieces of cake at a time. Quick cannons will not be able to save every piece of cake, as they are best at attacking a single target. This is OK since the last piece of cake is the important one.
4. Level 78. By this time your cannon setup will be very uneven, and there will be a huge weakness on the left side. It is still possible to convince the ants to walk into your strongest defense. Target ants walking through your weak points and they will learn to avoid it. (Screen Capture: http://www.billmanolios.com/forfun/antbuster4.jpg ).
5. Endgame strategy. When you're down to your last piece of cake all you can do is hope that the ant who picks it up will make a mistake, right?. Well, not completely. Try to keep as many ants as possible at low health. This way, when one of them grabs the cake it's already at less than full health. Meanwhile, continue to attack ants who walk through your weak spot to keep the other ants scared of it. (Screen Capture: http://www.billmanolios.com/forfun/antbuster5.jpg ).
6. Eventually, an ant with full health will grab the cake and walk it through your weak end. This can't be helped. All you can do is hope that it takes them a long while to figure it out. With this strategy I've managed to get scores consistently over 20,000. (Screen Capture: http://www.billmanolios.com/forfun/antbuster6.jpg ).
I'm sure this isn't the best Antbuster strategy out there, and I'm sure you'll get no joy out of copying it directly. I hope that reading this has given you some ideas...