Customers are loving Costco. But Walmart? Not so much, new survey says.

Customers were much more satisfied shopping at Costco than at Walmart, according to the study. Sam's Club also ranked a lot higher than its sibling.

• Costco topped a ranking of customer satisfaction with general merchandise retailers.
• Walmart placed last in the category, while Walmart-owned Sam's Club placed second.
• The annual survey polled nearly 36,000 customers and distilled responses into a 100-point scale.

Customers are pretty thrilled with Costco, but Walmart isn't getting that same love.

The Issaquah, Washington, wholesale club topped the American Customer Satisfaction Index ranking of general merchandise retailers with a score of 82, up one point from the year before, when it also placed first.

Meanwhile the mega retailer from Bentonville, Arkansas, came in last place in the category with a score of 70, down one point from its last-place finish the year before. The survey ranked 19 leading brands. Smaller brands got a combined score of 77. 

The annual survey polled nearly 36,000 customers last year distilling the results into a score on a hundred-point scale for various retail categories. Neither Costco nor Walmart responded to requests seeking comment on the survey results. The study looks at numerous "benchmarks" of satisfaction, ranging from convenient store hours to accurate pickup-order fulfillment, merchandise variety, and store layout and cleanliness. 

Wholesale membership clubs fared better than other types of general retailers, with Walmart-owned Sam's Club and BJ's Wholesale Club coming in second and third place behind Costco with 81 and 80 points, respectively.

In the supermarket category, Costco lost out on the top spot to Trader Joes, while Walmart still trailed the pack.

Across the general merchandise category overall, retailers made year-over-year improvements to their mobile apps and online order pickup processes, while issues like customer service, availability of inventory, and checkout speed deteriorated.

Costco's employee handbook says that superior customer service is its "most critical commodity," going so far as to require that front-end workers "greet every member with a smile."

Meanwhile, Walmart's decision to increase its reliance on self-checkout technology has increasingly drawn the ire of shoppers who are frustrated by the lack of staff.

Do you shop at  Costco or Walmart and want to share your thoughts on the survey? Get in touch with reporters Ben and Dominick via email.