I think it depends if you have Amazon Prime/Mom. I prefer Amazon because I buy a lot of other items from them and it gets me free two day shipping on my other purchases. And I set up monthly delivery of diapers/wipes so I get 20% off and they come at the same time every month.
I don't have any experience with Amazon Mom, but I will say that Diapers.com may have a fast delivery system, which is nice, but honestly, their prices really aren't that great of a deal when you compare them to Walmart or Target, and as far as formula goes, I've noticed Diapers.com is actually more expensive.
Diapers.com is too expensive. I used it for my initial 10 off first time user purchase but then noticed even with their eCoupon and cash back it was pricier than Target, where I get 5 off with my Red Card. We are going to try Amazon Mom since I have a Kindle anyways.
I love amazon mom. I have diapers delivered monthly and get the discount on them. I have prime so even when I need to order some out of cycle they arrive within 2 days, sometimes the next day. But then I use prime for just about everything else I buy, it's super convenient.
My Blog: Sewing, crafting, motherhood, computers, and random musings... Sleep is for the weak
Amazon supposedly owns diapers.com. But i like diapers.com even if they are more expensive because of fast delivery and superior customer service. Amazon customer service is a complete nightmare. Plus shipping can take a while, diapers.com is usually delivered the next business day.
Re: Amazon mom or diapers.com
Neither, use Costco. Boom!
My Blog: Sewing, crafting, motherhood, computers, and random musings... Sleep is for the weak