What's da scoop on feminized seeds?

Hey everyone! I need some help, I want to buy some seeds but don't know exactly what to buy, regular or feminized? Does anyone know if feminized seeds really work, are they garunteed to be female. Because I Would defintely spend the extra cash for sure if I knew that they would turn out to be females. Any information would be great. Thanx...

supposedly there is an increased risk of hermies if you stress them out

^^this is true...

but I've also had 100% success with fem seeds...never herm'd