Molly are less aggressive, it can live in brackish water or fresh water too. I have some living in fresh water happily with guppy in my planted tank...
Mollies are very peaceful fish and will only ever get boisterous with each other if anything, i was told by a man who had kept them a long time that they either like brackish water or super super clean water beacuse without the salt they become prone to fin rot. also there nice to have in a range of coulours, Gold, Silver, Leopard, Dalmation etc