@Aries lawyer’s answer, in short: it depends—on the purpose, or product category, rather; on the kind of intended use etc.
given that this is a thread about shoes and boots, i take it that properties of leather used for upholstery aren’t going to be of much interest to most.
keep in mind that despite my previous job mentioned above i neither am nor do i consider myself an authority of any sort on the matter, i just voice personal preference.
i am located in germany; there is a highly recommended website run by a german tanner who also serves as an expert for a regional branch of the german chamber of commerce and industry, called stefan banaszak: lederpedia (in german only).
also a good reference is leder-info (in german, english, french and polish), it includes informative illustrations and videos.
for english speaking folks, leather worker and american leather chemists association provide good info (the latter should be responsive enough to people who inquire by email).
the problem nowadays is that everybody chimes in and speaks their piece online, half truths, misinformation, facts all wonderfully blended together. try separating the ingredients of a smoothie.
here is a nice example of what i mean:
quite the mix, really! i especially like his interjections of »you know« when he doesn’t know how to specifically address something. (i just watched the first four minutes).
just for clarification: if you want info on leather (or any natural resource/raw material), go to the respective industry or association/union web sites, where there is no hidden agenda or veiled interest in regard to the information shared.
vendors, manufacturers, retailers, and so-called »influenzas« (because this hobby and non-job spreads like a disease) will tell you all kinds of fluffy stuff, because they want to make money, ideally off of you. if you want reliable information, always search for sources that earn their money elswhere, so they have no reason selling you ducksoup.
full grain, yes.
most expensive if required without defects, yes.
better than corrected grain? not so fast.
up to this point, this is all about choices regarding appearance, not durability or material quality.
see @CrashTestBrummie’s informative post on veldtschoen construction boots in the »edward green« thread at style forum (great pictures, and now i know who beat me to the punch on these beva boots when they were offered on ebay!): comparison of zug leather
edward green is not the cheapest of makers, yet the boots in question sport corrected grain leather (as do my hobnail boots and tecnic shoes above, vintage lotus boots and so forth). the leather is still very good and not worse than full grain. again, different purpose (pattern, uniform appearance), that’s basically it.
good entry on the shoe snob blog: myth buster: corrected grain is always bad
now, split grain … yes.
split grain is a cut corner, and less durable than full grain or corrected grain. you will find countless self-proclaimed fashion aficionados lecturing you on how inferior this layer compared to the former two is, while at the same time drooling over suede and its appearance and softness … but here’s the shocking revelation: split grain is suede.
the reason i mention it is this:
viberg chelsea boot for some € 640, selling for the same price as grain leather, nice one.
couldn’t find info on whether it’s full grain or corrected grain (which more likely).
not a viberg fan myself, obviously: they’re mostly about marketing hype and price hiking to my mind (i read a few interviews with brett viberg which i quoted in the thread some years ago).
the area from which you take your pick is important, because the characteristics vary depending from which part of the hide you cut your piece.
take a look at the soles of your feet and at the crooks of your arms—very different skin.
for most shoes the shoulder part of the cow hide. belly is too stretchy and uneven, more suited for accessories or upholstery purposes. for hiking and hardcore boots that are supposed to make your feet bleed, the butt (and make them real thick, too). you can influence a lot of the characteristics with tanning techniques as well.
hope that did at least partially answer your question.
add-on: i’ll post pictures of my vintage boots later, only 3 or so cost more than € 100 - € 120. many were not cared for particularly well. some are pretty stiff, some are still pliable and supple. but all are very much usable and wearable from an upper leather perspective (quite a few of them need resoling).
if you take into consideration that they’re all between 50 to 80 years old, that’s proven good leather—and it needn’t be expensive, either.
of course, priorities were different then, and you didn’t have an entire crowd (myself included) fixated on »heritage« and rugged-looking footwear. the irony is that the original boots and shoes were meant for work and physical labor or had to serve a specific purpose (military, safety gear et al). the aesthetics of stitching lines and sole decoration would have been laughed at, as they are not indicative of or relevant to material quality and functionality.
most of today’s customers just want that look, they have never worked on a ranch, oil platform or in a factory (as a student, i worked in one, very important experience), so they don’t understand the history behind the design and concept of the particular shoe they’re after. or how a chelsea boot originated as a boot for equestrians … funny how times change.
cordovan (as a final point), is a pure luxury item, because it’s made out of workhorses ass cheeks, so there’s not much to begin with. all horse leather can be (and is) used for shoe production, it’s wonderful leather with a distinct surface and, later, patina. do you know how much a square meter costs at a tannery?
€ 40 (in words: forty euros), that’s less than cow leather (depending on the tanning) … i know, because i asked (specifically regarding cordovan), i could’ve literally taken a car load with me … but then again, i don’t wear shoes that big.