Whats the best Small speaker thats cheap

I was thinking of upgrading my NHT super zeros which I love! Any suggestions must be reasonable lets say selling for less than $ 600 a pair new or used or less Must be small in size too 12 x 12 x 12 approx. maximum. I am considering NOS NHT super ones . BTW I am also using an NHT Sub One so Bass is not an issue ! Thanks !