They are both great coatings you can go wrong either way. If you do go C. Quartz do the UK version its very similar to OC 2.0 and it has a faster curing time the regular C.Quartz.
Just to be clear... OC and CQuartz are completely different formulas. CQuartz being Silica (Quartz, SiO2) based and Opti-Coat being Silicon Carbide (SiC) based. Both products, however, will protect far better than any traditional form of protection (ie sealant or wax)
From my research on it (getting a new car soon so trying to figure out what to do to it) CQ does not seem to be compatible some PPFs like XPEL (though if you don't have one this is not relevant), but other than that I think the biggest difference is CQ lasts ~2 years (warrantied for 2) while Opti-Coat is warrantied for 5 (or forever under
certain conditions).
Just making usre you are on the same page...
CQuartz FINEST includes a warranty for 2 years and
Opti-Coat PRO has the
option to purchase an additional warranty in the term of 5 years of lifetime (for brand new vehicles). Prices vary based on the installer. The consumer version of CQuartz and Opti-Coat (2.0) have no warranties associated with them.
As far as PPF - I would bet that any clear bra installer will advise you to have nothing on the paint at the time of installation. Regardless of what a coating manufacturer has stated. Chances are it has not been properly tested... there have been mixed discussions about this among CQF installers. General consensus is that no coating should be applied prior to PPF.
With that being said, I explain the coatings to my customers as follows:
CQuartz Finest is the thickest, glossiest coating on the market. It provides outstanding protection while also offering great durability and shine. This product is best suited for an owner that will continue to maintain their vehicle to the highest possible level and will have their vehicle polished and protected every couple of years. (note: CQFinest can last much longer than the warranted time of 2 years with proper maintenance. It is simply a fact that most cars can benefit from a routine polishing every couple of years to remove light surface defects and maximize the gloss yet again.)
Opti-Coat Pro also provides a great layer of protection that will last an incredibly long time. This product is more suited for an individual that simply wants to know his/her vehicle is protected to the highest degree, but doesn't necessarily want to go through the process of having it polished and kept up over time. This product will help your painted surfaces last longer without much work from the owner.
(note: if a warranty is chosen, the owner MUST maintain the vehicle according to proper detailing methods or else the car can be considered "abused" and the warranty is void. Something as simple as letting the dealership wash the car can void your warranty.)