Here's a head-to-head comparison of Guiliano "Mild Garden Mix" and Mezzetta "Italian Mix Giardiniera." I happened to have both of them in the pantry and decided to compare the two. Guiliano's giardiniera is usually found at Ocean State Job Lot, so it's fairly inexpensive. I buy Mezzetta's product at either Stop & Shop or Coronna's Market (my neighborhood corner store and butcher shop.)
Like many other Italian-Americans, I grew up eating giardiniera. It always has a place at family gatherings, and Maryanne and I put a jar of it on the table whenever we're serving a standard tossed salad, because there's nothing like a good giardiniera to wake up a boring bowl of leaves. And I hear that they use it as a sandwich topping in Chicago which really shouldn't surprise me given all the crap they pile onto hot dogs there, right?
My favorite part of the giardiniera is cauliflower. I don't have much use for cooked cauliflower as a veggie, but if it's pickled and still crunchy, I could nom the hell out of it all day. Both Giuliano and Mezzetta are mostly cauliflower. But Giuliano seems to cook the hell out of theirs while somehow, the Mezzetta cauliflower is crunchy and awesome. Actually, these qualities come up so often I'm not even going to mention it again beyond saying that the veggies in the Giuliano version are universally cooked and soft, while those in the Mezzetta are crunchy and don't taste overprocessed.
Giuliano is also a hell of a lot sharper than Mezzetta. They use a stronger vinegar solution and it shows. Usually, I have to give the Giuliano "garden mix" a quick rinse under cold water to get rid of some of the highly acidic flavor. Mezzetta giardiniera is a more tolerable strength, with a pleasant bite that doesn't threaten to kill your mouth.
I guess where you can see where this is leading. A good giardiniera is crispy pickled heaven, and a bad giardiniera is just face-collapsing vinegary pucker. Mezzetta is very good indeed. Guiliano is not quite bad, but it is sub-optimal. Given the choice of the two, it's Mezzetta all the way.