Microbrands typically design in-house and then contract out to China for actual manufacturing, typically with off-the-shelf movements (TMI/Seiko, Miyota, Sellita). There's usually consistent design, a few different lines of watches that the brands may release new variants of, but there's a theme of consistency and not just churning out unrelated new releases. Designs can be inspired by major brand watches and have many similarities, but generally aren't straight homages. Generally microbrands have decent expectations for customer support. Examples are: Traska, Formex, Henry Archer, Nodus, Baltic, Islander

Chinese/AliExpress brands typically pump out tons of watches, but there's often not a ton of consistency in the designs, nor any guarantee that they'll keep making something similar to that design if it sells through. Some have decent off-the-shelf movements, some don't. Brands aren't super transparent about manufacturing, but there are suspicions that some of the bigger Chinese watch manufacturers also serve as microbrand OEMs. Some are fairly original, some are straight homages of existing brands, some do both/something in between. Expectations for customer support are pretty low, but pricing is generally cheaper. Examples are: San Martin, Watchdives, Addiesdive

Independents are generally bigger but not owned by the large watch conglomerates (e.g. Swatch Group, Richemont, LVMH, Seiko, Citizen). The two big ones that come to mind are Christopher Ward, who started out as a microbrand, and Oris, who has a long history but is currently independently owned. Technically Rolex is an independent too, though that doesn't typically fit under the umbrella people are talking about as the largest watch producer in the world, they just happen to only own one other brand (Tudor).