TARGET!!! I have 2 girls...my youngest is still in diapers and my oldest occassionally wears a pull-up at night. I have bought Target Brand diapers (once they get size 3 & up buy the boxes, they are a little cheaper) for both of them since they were born...I LOVE them, and have never had a problem with them. I went around to (ToysRUs, Walmart, BabiesRUS, Costco) and did a price comparision...yes, I'm frugal. :) Target Brand was the cheapest. The only time ToysRUs or BabiesRUs were a little cheaper (.01 per diaper) was if they had a Buy One Get One Free Sale. Also, even with my oldest occassionally wearing pull-ups, if Target doesn't have Pampers or Huggies Pull-ups on clearance (CHEAP), then I buy the Target Brand pull-ups as well and they are great too! I also use Target Brand wipes, they are great as well.
As for Diapers.com, they are only cheaper if you want name brands (Pampers, Huggies, Luvs, Seventh Generation, etc.)...they do not carry a "generic brand."
Also, I know that a lot of moms that have boys have experience with certain diapers working well for girls, but not for their boys. But, I have a friend with 2 boys and my sister-in-law has 2 boys and both of them use Target Brand diapers on their boys and LOVE them and have said they have never had a problem. So...there you go...great for your girl and boy. :)
Good Luck...finding what works for your little ones, as well as your pocket book. :)