I don’t use much butter, so when I buy it I get the cheapest salted butter available. Is it really any different than more expensive brands? I know there are specialty butters infused with various herbs, but I’m speaking of simple unadulterated butter. Do more expensive ones taste more buttery?
In my limited experience they can definitely taste different. Whether that difference is better seems to be a matter of opinion.
If you are making cookies with it, go for cheap. If you’re making biscuits and want to put butter on top, consider trying some expensive stuff as well. You may not like it at all, but at least then you’ll know.
At the grocery store I work at, I’ve found that our store brand and the local name brand (Darigold) are pretty much interchangeable. On the other hand, I can definitely taste the difference with brands like Kerrygold.
I also find the store brand and brands like Land-O-Lakes to taste the same.
I also find Kerrygold stands out, and is better for spreading on toast or Irish Soda Bread.
One thing to remember about butter in the US is that the store brands are probably trying to be as similar to Land O’Lakes as possible. Since Land O’Lakes is the top selling brand name, it makes sense for store brands to copy it, and they are probably doing a reasonable job copying it at this point.
Sometimes, the store brands are the name brands in different packaging. But I don’t know whether that’s true of butter.
Wait, y’all buy butter?! 
I didn’t read that thread, because I’m not so concerned with COOKING with butter. But now that I’m looking at it, it’s not just about cooking.
My experience is pretty much this. If I’m using it as an ingredient, it’s whatever is cheapest. If I want taste, yeah, Kerrygold is better, but IMHO not better enough to justify the additional price. I usually buy the Kirkland butter in multipaks and freeze it all, using it with one defrosted stick at a time.
Alton Brown of Good Eats fame indicated that ‘fresher’ butter was more important than brand name butter in that the butter that was most recently produced (or defrosted) made a noticeable different, perhaps in chances for the fat to pick up funky flavors. I will say that the best butter I ever had was 20ish years ago when a family member who had a few head of cattle did an old fashioned butter churn, and both the milk and butter were less than 24 hours old. But even then, how much of it was in my mind?
Of course I buy butter, what should I do, make it myself? Where do you imagine I could keep the cow in the middle of the bloody city? Or you mean I should steal it (the butter, not the cow)? Because surely you are not suggesting I should buy margarine?!?!? 
As an ingredient for cakes, sauces etc cheap butter is OK. For spreading on bread something more expensive is worth it (some placebo effect may be going on here). I usually freeze the expensive butter in small cubes: it lasts forever and thaws quickly. The cheap one I freeze in 125 g portions (in Europe butter is usually sold in 250 g packs: I put half of it in the fridge, the other half in the freezer).
For cooking, I typically use Land-O-Lakes unsalted. For eating, I stick to Kerrygold salted almost exclusively. I find it to be more “buttery” and “creamy”, for what it’s worth, although Land-O-Lakes salted was my go to for this for decades prior to trying Kerrygold.
Whenever I’m traveling through Oklahoma, I make it a point of stopping by the Amish store and buy a few pounds of their butter.
Best I’ve ever had.
Grass-fed butter will taste better (or will have a more complex flavor), and it’s better nutritionally. Kerrygold is not a true grass-fed butter.
You can really get into the weeds with butter. It’s like coffee or scotch.
Also, spreadable butter is an abomination and is not even butter.
You’d better not open my fridge, then: you might faint dead away if you see my sprayable I Can’t Believe It’s Not Butter. 
The least butter-like substance on the planet, but it gets the job done when I don’t want to eat a dry Eggo.
I’ve always believed, “Butter is butter.” I buy “Land O Lakes” unsalted, and that tastes great to me for cooking or for putting on bread. If anyone deems something as markedly better, please comment.
I’m pretty sure some of us have already done just that.
In all seriousness, did you read the thread at all?
Lots of people have commented otherwise.
Very many years ago my wife and I honeymooned in Scotland doing a driving B&B trip. First night we stayed on a dairy farm. The milk was so rich, I thought I poured the cream on my cereal. The butter was the best butter I ever had. Kerry Gold is very good but nothing compared to that.
BTW: The actual cream, probably if you stirred it 4 times it would have whipped. That was incredible cream. 