I’ve made a few homebrew subclasses, but only one full class, and I think I’d go with that- Warsmith.
It’s a martial class that forges armor and weapons from magical metals (adamantine, mithril, etc.; there’s 22 options, 12 of which are restricted to 3 subclasses (4 each)). He gains special traits while wielding his own weapons, such as being able to dual-wield two-handed weapons, extra combat movement speed, and action surges (one per turn) in exchange for exhaustion points. On top of that he can sharpen his own and other weapons during short rests. It’s basically a fighter-support/crafting artificer, that you need a lot of downtime for.
It’s a niche class, but I’d rather make one of my subclasses into reality. And the main one would be Windblade Fighter or Windwalker Ranger.
The Windwalker ranger is a supportive class. If anyone here plays Genshin Impact, it’s very similar to Venti as I drew inspiration from it. The ranger can use his spell slots to create temporary wind current areas that become difficult terrain, blocks projectiles other than yours, and amplifies or reduces fire, cold, and lightning damage within it, allowing it be used defensively against casters or for a big burst of damage if you work with a caster teammate. They can also fly when dashing and use the wind to impair disadvantage on attacks.
The Windblade fighter on the other hand is an offensive subclass that utilizes the wind in order to extend the attack range. They learn some wind-themed spells, like Fust, Feather Fall, Gust of Wind, 1 of each level 0–5, that they can cast innately once per long rest. Their main thing is extending their melee attack reach, getting 30ft when they take the attack action, instead of 5 or 10 feat. This increases to 60ft at higher level. The second part of the class is the same of the Windwalker, getting flying speed while dashing, and just in general at high level, and being able to impose disadvantage on attacks they can see.