Since I am an operations type, I would answer operations. Getting the product to the customer on time, in full, at the agreed upon quality and price all falls on operations, and being reliable at that is largely how customer satisfaction (or lack of dissatisfaction) is achieved.
I would argue that customer delight is more the role of sales and marketing. That special pricing, added feature at basic cost, special packaging, etc all falls into the sales and marketing equation. It is difficult for operations to do more than basic satisfaction, so delight is where sales and marketing really shine.

No matter how much a customer may like a salesperson or sales experience, if the operational side lets them down, they simply will not stay or refer others. After all, most customers value and pay for the actual product or service, not the sales experience.

I like to put the operations people of my business and those of the customer together. Let them talk about all things operational and build a common understanding of making our mutual supply chains link up. Still need to sell the whole idea, though.

Both are equally important and one simply compliments the other.

Collaboration on both fronts allows for a streamlined approach to gain the importance of each other to serve the client.

Do not however forget that when looking at ANY P&L that top line revenue is FIRST!

Therefore without sales and customers/clients there would be no operating side in existence.

We have to understand a company as one holistic system (based on the philosophy of W. Edwards Deming), there is not one part more important than another. On the opposite, the total level of performance is only as good as the weakest part of the organisation.

The correct answer to this broad question is "it depends." Even though sale personnel are "outward-facing" and have the ability to assuage even the most disappointed client, for a season, their are unable to retain clients if the operations team doesn't perform its value-added role (i.e., providing sufficient responsiveness, cost-effectiveness, and quality/durability/fitness-for-use). In some organizations, the unique excellence or proprietary nature of the design and or operating processes are so compelling that the sales function is fairly perfunctory. Such organizations often find ways to "go direct" to customers. Other businesses compete in fairly generic product/service categories where the sales effort and continuing outward-facing communication and care is THE vital difference.

I agree both are equal to a point. But if sales does not sell something operations cannot fix that situation. Likewise,if ops can help convert a bad or marginal sale to a happy customer, they will have demonstrated exceptional service and btw they should be compensated for the efforts accordingly. Retention is almost always a function of ops and so is onboarding a new customer,but sales needs to find and secure the business from quality customers for the business to be sustainable long term.