I personally love the look of a fully grown male filament barb with long streamers on the dorsal fin.
As was said above, the filament barbs will get a bit bigger, and will do better with bigger fish. They should be good if you ever do larger ca/sa cichlids.
Either way, you can't go wrong, though. They'll both do fine with Bichirs. Just decide which ones you like more, and go with them. Also, you might want to check and see how much denison barbs cost around you before making up your mind. They have come down in price in general, but are still very expensive in some areas (we're talking $20 per denison in some areas, and you need a group of 7+ for them to live comfortably).