As a similar recent newbie who has played enough games to feel like I have seen all the factories in action, my newbieish impressions of the factories from the perspective of someone who doesn't know squat about the meta are:
Shield- It has small shields on 1/2 the stuff and the other 1/2 is all about playing games with said shields. Has a strong lineup with thugs and rackateers filling out the bulk of your forces, felons to do close in heavy shooting and walking shields for big shields. The goal is to have a huge ball of stuff with a jillion overlapping shields and just roll around crushing everything. Really strong in as straight fight but dies horribly to gimicks(crawler bombs, thunderbirds, fire). Constructors have shields!
Spider- Spiders are all about being on the high ground. Ballistic weapons shoot further from high ground and spiders are full of things that have ballistic weapons and can climb vertical cliffs to get high up. Recluse is the bulk with its long range rocket spam and skrimshingness, just point them in the right direction and they do their thing. Hermit balls for cracking defensive positions and venoms for paralizying stuff that rushes you. Crab is basically a massive mobile turret, teraform it a spike so it can sit up high and have crazy range. Special mention for fleas, spam them everywhere. They are stealth with no HP and a tiny gun, but so cheap they can squeeze in everywhere. Most units are slow though so you get out maneuvered on flat ground. Construtors have radars!
Cloakbot- Everyone says do these because they are really strong, and they are. Glaives for running around harassing, scythes for gimick stealth gimicks, ronin for skrimishing, reaver for close in killing, knights for mixing in everywhere, sling for arty. Round it out with phantoms for god-tier skrimishing and this factory basically runs itself. Is capable of fighting anything. Also has a mobile area cloaker that hides radar signature, very useful for sneakyness. Contrstructors are cloaked!
Tanks- Everything is really big and scary and expensive. Learn how to auto-retreat before using these ones. Units are super straight foward. Drive forward, explode stuff, retreat before death cause your wrecks are worth as much metal as most other facs units x2. The main thing here is never losing units and healing what gets hurt. As long as your careful, you just kind of roll over other facs cause tanks hit so hard and have absurdly huge HPs. Wheeled so they die horribly on rough terrain. Constructors are tanky and have a gun!
Rovers- Like tanks but weaker and cheaper. Special notice of dominatrix, the unit that steals other units and is top tier gimick unit. Constructors....are kinda fast?
Jumpbots- Gimick factory. Everything in here does something weird. Read the details before you poke it. [urlhttps://zero-k.info/mediawiki/index.php?title=Jumpbot_Factory]Jumpbot wiki page[/url]. Constructors can jumpjet!
Amphbot- Strong on land, really strong with access to water. Has a solid lineup with Archers/ducks for fast harrass, scallops/buoys for mainline fighting and Grizzly for mainline fighting REALLY HARD. Has a couple of gimick units that you can ignore or use as you prefer. Constructors are amphibious!
Hovercraft- Only take on really flat maps, they fail hard on slopes that even tanks/rovers can get over, can hover over water or land though. Has very solid units, dagger scout hits hard, scalpel for really heavy hitting skrimisher, halberd can yolo past defenses into hostile base and then wreck things, mace is great at mainline fighting and lance is like a tiny little mobile death laser. Claymore is your gimick guy, he runs in and drops a bomb, then runs away. Constructors can hover!
Gunship/Plane/Boats- Don't take these as first factory as newbie. You will die in a fire. Gunships/planes are cool but one dimensional, you need knowledge to not explode.
Striders- For when you have been winning and winning and winning and just can't make the other guy finally die. Or rushing really early and making the other guy insta-die.