On the bio/non bio : bio means that contains enzymes, meaning that it will be very good in removing stains. However, some people might have sensitive skin and might develop a skin rash if swearing clothes washed with bio products.
On the residue: what type of detergent are you using? In my experience, residue is a problem mainly for powder detergent, where either it doesn't dissolve (too much product, poor quality product, too cold temperature). Is this the type of residue you are getting?