The huge advantage to Garden Grocer versus the other big service is that if you are including alcohol in your order, Garden Grocer will accept an emailed copy of your ID, and will leave it at bell services for you without you needing to meet them in person.
If I wasn't going to have a bottle or two of wine included in my order, I would just price out whichever service was cheaper for the items I wanted to get. But the advantage of GG being able to leave my whole purchase with bell services, while I am out enjoying a park on arrival day, is for me a real luxury.