Okay, then the small cories. But not those you find at ones in the pet stores. Like green ones or pandas or albinos.
Still, NO NEONS!!!
I still suggest Shrimp. Snails poop like mad. And they only clean algae, while shrimp will even eat wasted food or waste.
The vast majority (like 99.9%) of the corydoras available in the hobby don't grow larger than 3". Because they are stationary and don't move around much, they don't need a large footprint as say a very active 3" inch cichlid. The inch rule, as I've noted before, is a very loose guideline. Other factors must be taken into account, including diet and territoriality and activity. Generally speaking, herbivores and omnivores carry a lower bioload than carnivores. As noted, cory cats are relatively stationary fish, therefore they don't need nor want vast amounts of space. Neons are schooling fish. Since they won't fight like cichlids would, they don't need a set amount of space per fish to set up a territory. Both are omnivores. Their bioload is relatively small compared to many other types of fish.
I have 10 neons in my 10g and they are very happy (their color is so vibrant!). Even professional aquarists stock them in tanks as small as 10g. Please note the stocking lists I copied from books by professional aquarists.
101 Best Tropical Fishes by Kathleen Wood
10 gallon Quiet Amazon Pool Stocking List
Top Swimmers: 3 marbled hatchetfish
Midwater Swimmers: 12 neon tetras
Bottom Swimmers: 3 panda corydoras, 1 clown pleco
Here's another 10g stocking list from a different book, Freshwater Aquariums by David Boruchowitz (I really respect this guy a lot)
5 zebra danios
2 cherry barbs
3 cory cats
I also have in the same 10g 2 panda cories and 2 Venezuelan Sailfin cories (variations of Bronze Cories). In a cycled and mature tank with plants, this is a reasonable stocking.