I would deffinitely go with the clown loach get about 20+ and your tank will look amazing. Get something unusual for the top or something like african butterfly fish and some geophagus they come in so many amazing colours and body shapes and they are fairly placid chiclids along with some lowish lighting, bogwood and tall plants or java fern attached to the bogwood, sand substrate and that in my opinion is a very good looking 120gal tank. Thats what i would do.