Given its just that small size, id keep it neon tetras only. Let them have more of the space.
Only cories suitable for that tank size are the pygmy cory species, but they will use up some midwater space too, so that would infringe on the neons space for swimming.
Now, if you upgrade to a 20 gallon long, move the neons there and could do a nice shoal of cories in that
This tank then could house some microrasboras like chili rasboras, boraras, or my favourite the kubotai rasboras... theyre super small and would do fine in the space. Go for a nano tank!