personally, i enjoy K2 which is chemically enhanced herb. you can find this at many gas stations. other names for it will be "lol" or "omfg"....just a warning, too much of it will make you pass out.
From what I have heard, any medicinal strains are. Other than that I have heard well from "Haze" strains. I only dabble with small time strains like AK-47, White Rhino etc.