i have mollies with bettas and they do great, maybe im just lucky, but ive never had a problem. also, it depens on what type of algae eater it is.......chinese algae eater is a no go. aggressive as jupiter said, i wouldnt put them with neons unless they are full grown like at least an inch, but me personally i wouldnt trust neons with them. guppies, no way....
a sorority tank would be ideal