ember tetras are bigger than neons...Neons need a bit more room than a 10g can provide. Move those 10 to a 30g tank and you'll see much different behavior, IME.
For a 10g, Ember tetras would be great. Also, if you can find Microrasboras, they'd be good as well.
Harlies are ok, though they are pretty active. A 20g would be a better minimum for them.
neons are fine in a 10 gallon.
