My sister works at a local grocery store and I was really curious as to which type of bags are most preferred by her customers.  She says that plastic bags are much more convenient for people and they choose these types of bags the most.  I asked her which type are more expensive and she said that she was not sure, but she did know that they get their plastic bags wholesale.  I like the plastic bags because I am able to reuse them for many other things.  I think that it is really a personal choice and some choose paper for other reasons.