I'd like to weigh in a bit and provide some information. I have used a good variety of coatings but certainly not all of them. I have used CQUK once. I have not used the new Opti-Gloss but have used plenty of the old OC2.0
Now down to your list. I am going to reference the PBL paint coating V1 as well since I have used it.
The DP paint coating is a great coating to get your feet wet with. It is also cheaper than the others so you could include this as an entry level coating for clientele if you so wish. However the looks and durability is not on par with the other PBMG coatings IMO.
The PBL paint coating V1 is a great product with good durability and ease of use. It does change the look of paint and darken it a shade IME. If you really want to AMP up the shine, gloss, depth, etc PBL Synergy does dramatically do that in my experience.
What I personally don't care for with the DP coating and PBL coating is the added machine step needed to cleanse the paint from previous machine polishing steps. This method uses a machine step to cleanse the paint instead of using an spray and wipe such as IPA, Eraser, etc. Keep this in mind.
Now we arrive at the new BlackFire Paint coating. This product gets my vote over the other coatings listed and that I have used. Surface prep is the easier method with the spray and wipe technique. Ease of use will come down to personal preference of the user. This product is thin and has the consistency of water. PBL applies from a mist.
I will say that the darkening effect is more noticeable and pronounced with the BlackFire product. Gloss, depth, shine etc will be even more pronounced when you apply BlackFire Midnight later on. Of course you could also add some Midnight Sun Paste, Souveran, or Synergy.
Now on the back side of things, I really like the supporting maintenance products for the PBL paint coating such as the dedicated shampoo, coating detailer, and coating booster. I would really like to see an addition to the BlackFire lineup to support the coating that maintains the "Synergistic Compatibility".
I hope I didn't get too far off track or confuse you.