Custom made orders are fun, because of the close contact with the customer.
That being said.... I prefer ready to ship listings.
I prefer making things that I want to make, when I want to make them, listing them, selling them, and shipping them within 24 hours.
That means I am in full control and I do what I do, when I want to do it.
With custom listings, the customers have control. They more or less control what I make, how much I make and when I make it.
(I have chronic health issues and can only be active for a couple of hours a day, on a good day, so I prefer ready to ship listings.)
In general I think a mix of both custom listings and ready to ship listings work best for most sellers.
Ow, and I forgot this: most purchases on Etsy are impulse purchases!
You loose out on those sales if you only have custom listings.