Any advice on buying quality vinyl

"I think it is impossible to generalize."   +1(a plethora of variables)   

I think it is impossible to generalize. The attraction of the better audiophile reissue labels is new, usually clean playing LPs that may or may not sound better than an earlier pressing. It depends on the particular record, which usually means you have to dig down and learn about different pressings, compare them or rely on anecdotal comments from other people who have made such comparisons. I don't think there is one easy path.
The biggest limitation can often be the selection of material offered by the audiophile approved labels- in many instances it is the same stuff, reissued repeatedly, because there is an established market for known "best sellers." That said, if you need to fill out your collection of certain rock, jazz, etc. they are worth considering. 
But, if you want to push the envelope and look for less well known records, or are seeking out some records that have never really been bettered by modern masterings, you are in the world of older pressings. It is, for me, a continuing education, not just of the minutiae of pressing details (and how that correlates with sonics), but an ongoing exploration of different music that I wasn't familiar with, or simply ignored. This journey has led me to a lot of music I was unfamiliar with. 
For example, I had lost interest in straight ahead jazz. I had many of the warhorses- great records, to be sure, but I seldom listened to them. A friend turned me on to "spiritual jazz," a movement that took place in the early '70s after mainstream jazz became a dead letter commercially. I started to tap that vein- records from small labels like Strata East, Nimbus West and even smaller, private labels. Some have been reissued (Pure Pleasure has done a number of them, and despite their opaqueness about source material, the ones I've bought sound quite good and are far cheaper than the original pressings, condition is less of an issue, etc.). Speakers Corner did a remaster of Herbie Hancock's Crossings, another eclectic spiritual jazz record that is cheaper and in my comparison, sounds better than a time capsule original US pressing.
I think you have to figure out an entry point. Are there particular records you are seeking? You can research anecdotal comments on "best" pressings. Are you looking for new to you music? Lot's of things to read, and sample. There are any number of lists, including comments here and on other fora, about what people like.
This sounds like work, but it is fun work, and you learn quite a bit along the way about music history, pressings and your taste. I am also listening to a lot more different music than I did 20 or 30 years ago and really enjoy finding things that are a little off the mainstream path. Treat it as an adventure and you will be rewarded accordingly.

Uberwaltz, I reached the same conclusion doing a test of three recordings of Madman Across The Water.  I played Tiny Dancer from all three records and the one that sounded the best , save for pops and clicks was my original Uni pressing from way back.  How are you able to determine what is an original pressing?

I only buy original pressings that includes some Japanese first release pressings, mostly from 70s. Yes, I have just a few records that I would call Mint condition, most are strong VG+ and NM/NM-, and I have a few rare very playable VG records. Prices I paid vary from $0.99 to $150, about $30-$35 on average plus shipping. 

No Better Records is not hype. I've got a White Hot Stamper of Fleetwood Mac. People can whine, argue, whatever about the cost being worth it. What they cannot do is find anything better. The best of what they have is so much better than ANYTHING else I have EVER heard it is not even close. Honestly, I would never in my life have thought anything on vinyl, tape, or otherwise could even be that good. Granted I have never heard a studio master tape. Certainly nothing pressed can ever be any better than that. Whatever. Like I said, bring on the whiners and deniers, its just inexplicably unbelievably awesomely good sound. 

That said, the next big takeaway from this is they are right, no two records sound the same. Once I compared my run of the mill Fleetwood Mac to the otherworldly good WHS I started doing shootouts with some of the other dupes in my collection. The results so far are there are indeed no two copies yet that I have compared that sounded the same. ALWAYS there is one that sounds better. Not a little better. Not like you have to strain to hear. I'm talking like its darn obvious and right away. So obvious in fact that one time I even knew the copy I was playing was a dud and I hadn't even heard the other copy in over a week!

The dud by the way was a BRAND NEW Analogue Productions copy of Linda Ronstadt's What's New. A fabulous George Massenburg recording mastered by the legendary Doug Sax at the Mastering Lab.... RUINED by Analogue Productions! I mean I could only stand a few minutes then yanked it off and replaced it with my worn out old used record copy which sounds a whole lot better. Strings have just the right amount of bite, Linda's voice is THERE with enveloping acoustic, on and on. Much better.

Every shootout I have done, if you can find a decent sounding (not even especially good, just decent) original old pressing I can just about guarantee it will absolutely kill any heavy vinyl audiophile reissue no matter how much they overcharged you for it.

I’d avoid both MoFi and Better Records. Absolutely seek out good original pressings, but no need to overpay to the level of "Better Records". Some of your cheapest records will turn out to be your favorite gems, after a good clean. That's part of the vinyl magic - don't give that up to the cash grabbers. MoFi have been really hit or miss (some can be good I guess). Some reissues can be great, but many of the "audiophile" reissues are so, so disappointing. Some RSD issues are great, but many are just lame. New music on vinyl can be lots of fun. Get used to DiscOgs for sourcing the rare and hard-to-find gaps in your collection, and also to scope out what pressings/variants are available with rough values & quality ratings.

Amazon can be really cheap & fast for new issues, but god help you if you like to receive your covers without dinged corners (at the least). Acoustic Sounds & Music Direct know how to properly pack vinyl. But I’ve been caught on the long end of a backorder some of the few times I’ve used M.D., so Elusive Disc probably gets highest ratings from me.

Acoustic Sounds is a good place to get records. Don't have any experience with the hot stamper crowd. I suspect they are more hype than anything else.

Ime great condition original pressings are still hard to beat.
Usually a good us clean and you are ready to rock.

I am sure you will get lots of varied opinions on this one.