Guardians are heavily armored and reward very little experience. They take a long time to kill, and the weapons they employ hurt a lot. Most players simply avoid Guardian drones.
Many a new player has met his first death upon meeting this model. The Aputech-5 mounts the infamous popcorn gun (called a flechette). It is a shotgun-style spray weapon. If you are too close to this bot, you will get hit. Distance control of between 150 and 200 meters is your best bet for staying healthy while scoring hits. A rolling tactic of any kind is only marginally effective; mix a two key strafe with actively varying your distance. As explained above, your time is better spent hunting something else.
The Fenrus R-18 is not a guardian to trifle with. It mounts flechettes and a gauss cannon. A two key strafe with distance control of 70 to 90 meters evades the majority of the damage. An attack roll is also effective. You'll need to close to somewhere around 75 meters to be able to score a hit on one. They come in pairs. The one redeeming factor of the Fenrus model is their low rate of fire.
The Devus D3 Guardian is the most fearsome guardian bot. The armor is high, and it will keep up with you if you backroll. It mounts Neutrons and Flechettes. The combination of Neutron and popcorn is about the most frightening combination imaginable. Do not fight it close, but it will not be satisfied to stay far away either. Flying within range of this bot causes it to attack, you won't even have to shoot it. It attacks in groups of four, and if there are fewer than four, Arklan Guardians join them to fill the ranks. If you do choose to fight them, expect to repair after every single kill.
Orne Guardians are large and slow. They mount dual gatling turrets. If you backroll, an Orne may never catch you. A two-key strafe is somewhat ill-advised; use an attack roll and control your distance to 70-100 meters. They don't attack alone.
Similar to the Orne, the Arklan Guardian mounts two gatling turrets. Since gatling and gauss fire is always thrown off with a roll, it is a safe strategy here. Arklans will attack you in pairs. Using an attack roll, pound away till it dies. Expect to be at it a while, Arklan armor is really something to see.
These bots only mine until they are attacked. They are heavily armored. Easiest way to kill them is to either stream avalons at cruise speed or stack the avalons. Once a single guardian is damaged, you will have a over five of them chasing you. Since they are armed with Power Cell Blasters, Law Enforcement Neutron Blasters, and Axia Accelerated Positron Blasters, your best bet is leave the sector after your avalons hit. Their weapons do not drop.