My experiences of the main players (having now bought over 200 of them in the last 4 years):
Pallas: prone to fill issues and other extraneous noises. When you get a good one, however, it is superb but I'd say a good 25% of them these days are significantly flawed. This company seems to go through periods according to vintage. Over a decade ago the quality was excellent but maybe about 4 years ago the quality started to go downhill. The latest pressings, however have (touch wood) been very good. But if I get a title that is New Old Stock and pressed a few years ago, chances are it will have problems.
The Old Vinyl Factory Hayes: Worst of the lot hands down. Even makes RTI look good. This company should be making plastic buckets, not pressing records. I've begged the record label that uses this company (HiQ) to go elsewhere (to no avail obviously). So bad that I now routinely buy two copies of any record pressed here, because the chances are about 90% that one of them will have significant fill and other assorted issues including whole sections of terrible clicks and pops - but fill problems are the biggest problem with this company. When I buy two copies, I digitise them and spend many hours fastidiously editing them so as to have a seamless performance without flaws (since sadly the label does not release high res digital versions of its titles).
RTI: As bad as they have ever been. The ORG reissues have terrible problems. I'd say half of them are badly flawed.
Quality Record Pressings: A breath of fresh air. Having bought about 35 of these, only two have ever warranted a return and one of those two was their very first pressing that had an acknowledged "official" issue. The second one had about 200 loud clicks on one side (one per revolution but there were no visible flaws to the naked eye and it was ultrasonically cleaned on an Audio Desk Cleaner before I purchased it. That said, whenever I know a title is coming out on QRP, I breathe a sigh of relief knowing that the chances of getting a dud are very low.
Optimal: My favourite alongside QRP and about the same in terms of quality and consistency.
I suppose I should add that I rarely ever return a record. I've probably returned about 4% of my purchases. If record has significant issue but I believe they can be rectified with my advanced editing skills, I will prefer to digitise it at high resolution than return it.