Choosing between Reissue and Original pressings

If I had to choose, in the abstract, between an original pressing and a
reissue, I'd choose the original (assuming, as you are asking us to, that it is
not impossibly priced). Boxstar is a good example. I like Janis Ian's
Between the Lines and have a number of copies, both originals and the
Boxstar 'audiophile approved' reissue. I fired that up a couple months ago
and thought something was wrong, it sounded flat and lifeless. I put one of
the old CBS pressings on, and whooosh! Back came the life. Ditto, on a
similar experience with a not so mainstream jazz recording of Amina
Claudia Meyers saluting Bessie Smith. The original, on Leo Records,
sounds very, very good- particularly the piano. I bought an audiophile
reissue to have as a backup. It sounds dead and at two removes by
comparison.
The difficulty with the originals (and in both cases mentioned above, the
originals came from an era that was not a high water mark in vinyl quality,
circa 70'-80's), is condition. Buying used, even 'mint' is not mint in my book-
noisy because of what it was played back on in the day, or worse.
I don't know why remastering engineers have to change the sonics in a way
that is sterile. Maybe it is the condition of the master tapes (assuming they
are going back to original tapes, which may be a big assumption).
In some instances, the reissue may be better only because the pressing
quality of the original was so bad. Here, I'm thinking of the Shelby Lynne
'Just a Little Lovin' record- the Lost Highway pressing is just unplayable. It
is defective. And the copies I had were not anomalies in this regard. You
have to buy the 'audiophile' version to get one that's playable. (And even
those have uneven quality control from what I gather).
I'm sure I could think of other examples where the reissue is acceptable as
an alternative~ but often that is because the original is impossibly
expensive.
How do you know which is better if you had a choice? You don't, without
playing it or relying on someone you trust. I don't necessarily trust
reviewers, having bought a few records based on positive comments about
sonics- either we don't share the same view on what sounds 'good' or our
taste in music is fundamentally different.
I've had decent luck finding some 'pop' records from the late 60's- early
70's that sound really good, but there may be copy to copy variability. Two
examples: the second Blood Sweat and Tears record can sound startling, if
a little bright; ditto a couple sides of Chicago II. (One of the sides on that
record sounds nasty, i can't remember which, and maybe it was my copy,
but even on the same copy, there may be differences in the sound from
side to side). Final observation re a well-known record: I have had
innumerable versions of Tea for the Tillerman, including the UHQR which I
bought new. The best is the pink label on Island, pressed in the UK. The
pink rim is also good. All the other reissues sound ''less good.' But the pink
label is a known commodity and is priced accordingly.
Sorry for the long post.
Postscript: the Classic reissues on 45 can be very good and in the case of
the RCA 'dogs' are quieter than the originals I have. But I had a lot of QC
issues with stitching and 'no fill' and quit buying their records at one point
when they were still newly and cheaply available because I didn't want to
put up with bad pressings. So, even where there could be an improvement,
it turned out to be illusory.

I don't know if there is a general rule of thumb on which pressing or country of origin is best. Others with more or different knowledge are free to contradict me, but here's what I know:
on certain records, I suspect the first pressing is more desirable for collectability than sonics;
there's all kinds of lore (some of which may be true) about the matrix numbers, pressing plants and mastering engineer inscriptions- I certainly couldn't generalize about that, or point to particular examples where I have compared one old record to another and concluded that a later pressing from a different plant sounded better than a first pressing; I know there were preferences among RCA collectors, but I haven't done enough comparisons to make a valid judgment. I do remember comparing a white dog to a shaded dog of one old RCA classical record and the white dog sounded better- this was quite a while ago.
as to country of origin, my guess is to look where the record originated from- Mercurys are probably better from the US; UK stuff, like Island, probably UK. I think out of all the Pink Floyd Dark Sides, it is the UK original that gets the votes for sonics.
As to Japanese reissues, I think the key there was that a lot of records were made of crap recycled vinyl in the late 70's-80's, and the japanese were touting virgin vinyl. But, given what they were working from in the way of masters, I wouldn't necessarily say a japanese reissue is hands-down better.
Does your last question mean, can you hear the difference? I gave you a couple of examples in my earlier post. And the originals were pretty standard issue, generic pressings from major labels of big selling popular records.
As time and my system has improved, I have found most of the MFSL records (old ones that I bought new back in the day) to sound very average, nothing special. I think most were mastered at that time by Stan Ricker. This was true for the UHQR as well as the 'regular' 1/2 speed masters, of which I have quite a number.
On Rumors, I really never grooved on later FWMac, i do dig the early Peter Green stuff, but the copies I have of Rumors are original issues as far as I know (I will double check for you), and they sound pretty good.
I love Muddy Waters, but I never got why the Folk Singer record was so highly regarded musically. I prefer his smokey electric blues thing, but that's a music content issue, not a pressing issue.

GMC, the problem with better records is that there are no guidelines other than his ear in picking out the good sounding copies. he trashes most of the well-known reissues which may be right, but after that, he provides zero info on particular release versions, stamper numbers or other indicia of what particular copies sound good. Aside from paying 499 or more for a garden variety mass produced major label issue. Hell, for 500 bucks I can buy quite a few copies and do the same thing. Time-saving, perhaps. And funny to read his comments. But not sure there's real, useable positive info there on what to buy, more negative on what not to buy (which, as I recall, is pretty close to everything except those selected by him).

GMC- we are on the same page. I like your wall of vinyl at home.
Viridian- excellent point. I did touch on it in my earlier post here, but didn't
spell it out as you did. Which may be one reason why mastering engineers
have to make dramatic changes in the sonics? Or is it also catering to a
brighter, 'clearer' sound that people may prefer after getting used to digital?
Part of the death of good sound is complex multitracking, where having all
the musicians in the same room and a sort of bleed through of the acoustic
is lost. That may be why some of the 'audiophile' recordings like D2D sound
good, apart from skipping the tape altogether. (unfortunately, most of the
natively 'audiophile' records leave me cold, musically).
AudioTomb- are you talking about those new Apple reissues on vinyl?

Ralph: any way to discern which records used the Haeco CGS process?
Are they early stereos that had the legend that said something "fully compatible on mono players, but for best results, play on a Stereo"?
Is your last line a tease?