I'm a member of both Costco and BJ's. Here's why Costco beats its rival hands down.

What is there even to say about the wonder that is Costco's Kirkland brand?

Offering everything from toilet paper to decently high-quality wine, the low-cost brand is one of Costco's biggest assets. Per a report from earlier this year, it accounts for almost a third of the wholesale club's sales.

BJ's equivalent exclusive brands — Wellsley Farms and Berkley Jensen — are generally of decent quality for many offered items. But they have nowhere near the cult following that Kirkland does.

While store sizes aren't standardized, depending on the availability of space in a particular location, Costco stores are, on average, larger than BJ's stores.

The average Costco store is about 145,000 square feet, according to the company's 2018 annual report, while BJ's layouts are much more compact, ranging from 70,000 to 130,000 square feet, BJ's president and CEO Chris Baldwin told Retail Leader.

Consumer Reports found in its 2018 supermarkets survey of more than 75,000 shoppers that a majority ranked Costco slightly higher than BJ's in general.

Factors cited included the high quality of Costco's goods, its meat and poultry in particular.

One of the lesser-known perks of a Costco membership is its member prescription program. It's a value-added benefit of the annual membership fee that enables eligible members and their dependents to buy their medications for a lower price.

On the flip side, BJ's opted to drop its in-store pharmacies back in 2007.

While it's not explicitly spelled out anywhere, Costco has a notoriously lenient return policy on all non-electronics items (electronics returns are accepted within 90 days of the customer receiving the merchandise).

In fact, a story about a woman reportedly returning her dead Christmas tree to Costco on January 4 went viral back in 2018.

BJ's, on the other hand, specifically will not accept non-grocery merchandise that isn't in "new condition." Anything purchased over a year before will not be considered new. For electronics, BJ's has the same 90-day rule as Costco.

By the American Customer Satisfaction Index's measure, Costco beats BJ's in terms of customer satisfaction.

This is obviously subjective and will vary from store to store. For example, the crowds at my local Costco are regularly swarming, whereas the BJ's near me is usually far less chaotic. Still, in aggregate Costco comes out on top.

Sometimes, you just get hit with an undeniable hankering for an incredibly cheap, incredibly large hot dog. And when that urge strikes, Costco has its shoppers covered with its infamously inexpensive food court, which purposely keeps its prices low in order to ensure a better shopping experience for customers. A hot dog and a drink will run you $1.50, and you can get an entire pizza pie for $9.95.

On the other hand, BJ's doesn't have a food court. Instead, the wholesale club partnered with Dunkin' Donuts back in 2016, replacing many of its in-store food courts with Dunkin' kiosks. Good if you need a quick caffeine fix, not so good if you're craving a frankfurter.