Due to how new the class is, there are currently only 4 subclasses of Artificers, by far the fewest options of any subclass. That doesn’t mean they are the worst, however- they have a lot of flexibility within those 4 subclasses. These are the inventors and creators of the D&D realms.
Alchemist
(Tasha’s Cauldron of Everything p.14, Eberron: Rising from the Last War p.58) Alchemists are really good at making potions. They can make one or more random ones each morning, can add some potion-ish effects to the spells they cast, and get some extra spells and resistances that are also potion-ish. If you’re all about potions, this is the subclass for you, my friend.
(Tasha’s Cauldron of Everything p.15, Eberron: Rising from the Last War p.58) Armorers are all about the defense; these artificers make crazy good armor, which only gets better as they level up. Armor with really powerful weapons in addition to being really good for defense. We’re talking Iron Man stuff here.
(Tasha’s Cauldron of Everything p.17) Artillerists focus on amping up the ranged attack side of things, including making their own pet firearms which scuttle around, firing at things for them. Meanwhile, they are also improving their own personal ranged weapons. Pew pew, this subclass is all about shooting from a distance.
(Tasha’s Cauldron of Everything p.18, Eberron: Rising from the Last War p.60) While Artillerists make pet firearms, Battle Smiths make solidly dangerous pets called steel defenders, which are ready for battle up close and which can be used as mounts. Kind of like having a pet tank.