I think it's always better to use fresh, but as long as there is nothing extra added, frozen work just as well. I found that I really liked having frozen fruit on hand during the months where the fruit was not as widely available and I also liked keeping frozen veggies on hand just in case I didn't have any fresh.
I think that veggies yield the most food, especially sweet potatoes and squash. I always needed a lot more fruit to get a nice-sized batch. Bananas and avocados yield a good amount of food too.
Lenora & Chris 01.16.10
DS Brandon 05.13.07
DS CJ 10.06.11
*Co-moderator of January-June '07 and September '11*
Fresh and frozen are pretty much the same because the frozen foods are flash frozen when they are at their peak freshness/ripeness. Depending on how far the foods have to be shipped, frozen can sometimes be fresher than "fresh" foods. I buy fresh produce when it's in season, frozen when it's not.