I have some yoyo loaches and really love them. And they really love the snails I feed them. As far as aggression, I think it depends on the yoyo. I hear that they are the more aggressive of the loaches (lots less then skunks) but mine have not been a problem. A trio might work well for ya…
I have read that some of the "nice" speices of laoches that eat snails are zebra loaches, weather or dojo loaches, and possibly kuhli loaches. I am sure if you do a search and read up a bit that you can find which works best for you.
Sorry i can not be more help, but this should get you started...
Spunky