Kirkland Signature, the in-house Costco brand you'll see all over its warehouse-sized stores, sells a wide variety of goods, from Kirkland Signature maple syrup to Kirkland Signature spiced rum.

I find they're often twice the price of standard plain yogurt. So, to see which Greek yogurt is the best value, I tried store-brand versions from Trader Joe's, Whole Foods, Costco, and Wegmans. I ...