to me, it wouldnt matter. guppies are very colorful, very sociable and easy to look after, but they breed quickley and soon overpopulate your tank.
platies are hardy, slightley bigger then gups, come in many colors and are great fun to watch, but again breed quickley.
mollies are brackish water/ crystal clean freshwater. so regular tank water changes are a must. some nice colors, normal mollies or ballon mollies avaiable.
saying all that. i would prbally go for some nice guppy males, some female platies and possably either sex of molly. the bigger the groups, less aggression i find.