Either would be OK with Botia striata from the point of compatibility, but the tank size as Jeff mentioned is a factor here. And we don't know how many loaches you have. They must be in a group, I would say 4 is absolute minimum but 5-6 would be better. I have five in my 90g, along with five Botia kubotai which get a bit larger.
In the profile [click Botia striata] I gave 36 inches as minimum tank length, and I think that is best. A 20g long at 30 inches would be better than a 20g high at 24 inches. And here I am still on the loaches.
If you have 4-5 Zebra Loach in a 20g, for upper fish I would go with the rasbora because they are less active than any barb and this is always better in smaller spaces. I wouldn't suggest the dwarf species like Boraras brigittae (Mosquito) because they are so tiny the loach might eat them. The species in Trigonostigma would be better, and of these three the two slightly smaller best, namely Trigonostigma espei or Trigonostigma hengeli. The latter are my favourites, they are very attractive with that brilliant copper "axe". You should be OK with a group of 7 of whichever, if you maintain regular weekly partial water changes of half the tank and have live plants.