I've used both and I love the backpack. We got a actual diaper backpack, but we should have gotten a regular backpack with a lot of pockets. I find that I run out of space and number two isn't even here yet! When number two comes around I'll probably sell this one and just use another one that I have.
We used a regular diaper bag, then ended up getting a back pack when she was around 1.5. I love the book bag. We're gonna use the backpack for this baby.
I have a backpack diaper bag and I love it. We have the Baby Boom Spaces and Places backpack from Walmart. It has lots of storage space and it's easy to carry. I used a regular diaper bag with all my older kids and I wish I had gotten a backpack one sooner. I like that it doesn't slide off and it makes carrying the carseat so much easier.
Loved the backpack. Used with my son and will with this one. Makes for more hands free.