In an AI game, planet busters are a useless unit, except for schadefreude. By the time you get them, it should be fairly easy for you to capture any base you want, with a lesser investment of time and minerals. I can imagine a case in which, after a slow start, a powerful enemy has packed the monosoon jungle with bases and you can take out five or six with a single shot. But I've never needed to.
Choppers are the single most powerful unit in the game -- they're overpowered. Often a human player gets to MMI while the AI are guarding their bases with plasma garrisons -- in which case choppers can wipe out defenders faster than you can build infantry to drop into them.
Choppers:
* Can target multiple units.
* Can leave the field of battle and return to a base, completely protecting them from counterattacks (an amazing ability).
* Can travel long distances and cross water to attack your foes.
Again taking the worst case scenerio, a high-tech AI with silksteel AA troops (something that should happen rarely, if you know how to climb the tech tree); a carefully planned chopper attack is still devestating. Simply:
* Rip out the Aerospace Complex with probes.
* Kill any sensors with Needlejets.
* Equip your copters with gas pods (nerve gas isn't worth it in an AI game.
If this doesn't suffice, kill formers and lightly armored units to promote your copters, and switch out of wealth for a while.
Follow these simple precepts, and even Chaos Choppers should be able to kill a silksteel AA garrison.
Artillery is rarely needed in single player. Occassionally some jerk-off -- usually Yang -- will haress me to the point that I will build some, but usually it's a waste of time. The AI doesn't defend its bases well enough to need softening up.
Native units can be an early lifesaver if you've been focused on Builder techs, neglecting war, but later in the game, they're just too expensive.
Gravships, hovertanks, carriers; if you get these units, and the AI is still competative with you, you are a beginner. Don't be insulted! There is a sliver lining (there are two, in fact). First, not being an expert in an esoteric video game could reasonably a point of pride, and; if you are such a beginner, there are still a lot of exciting surprises in store for you playing our fav game.