Some people think the 'secret' of varnishing brightwork is in what kind of brush you use, or which particular product you choose to apply to your wood.
Some of the traditionalists may regard me as a heretic, because I use throw-away foam brushes, rather than the traditionally-approved, expensive "badger" hair brushes.
To those purists I reply that the famous Rebecca Wittman, who wrote the beautifully illustrated book, Brightwork: The Art of Finishing Wood, is on my side. She and I prefer the Jen-Poly brand of foam brushes. And it doesn't really matter which brand of varnish you buy, as long as it's a reputable one, with adequate UV filters.
Some of the better-known spar varnishes are Schooner's (made by Interlux, now owned by Akzo), Epifanes (Dutch-made), Flagship (made by Z-Spar, their top-of the line), Captain's (also made by Z-spar), and Awlspar (made by Akzo Nobel, the same company that makes Sikkens Cetol products). All of these are quality varnishes, with sufficient ultraviolet light protection, although they have different handling characteristics.
I would avoid the house brands of marine store chains – they tend to be of inferior quality, in my opinion, having observed the experiences of certain do-it-yourselfers who wanted to save a few bucks. Just remember that the real cost of any refinishing project is in the hours spent in labor, not in a few extra dollars paid for a superior product. Besides, after investing all that time and energy, don't you want the result of all your efforts to last as long as possible, looking its best?
I personally prefer Awlspar for buildup coats, because it's a quick drying, high-solids varnish with excellent handling qualities, and best of all, you have a 24 hour time window to apply successive coats without sanding in between. Professionals call it "hot-coating", and it will save you countless hours of unnecessary labor. I routinely apply four coats outdoors on a spring or fall day here in Florida.
Now for the greatest heresy of all: mention the word "Cetol" to many boaters, especially the traditionalists, and you'll be received with a look of disgust or horror. This is because they've only seen the misbegotten-from-hell results of an amateur job done by someone who didn't know what he was doing.
Granted, I've seen many a Cetol job that looks like someone used a dark, opaque shoe polish to finish his teak. I assure you that with a proper understanding of its handling, even the novice varnisher can produce a top quality finish with a two-part Cetol system, that looks almost as good as the best varnish job.
I use traditional spar varnish on most of my jobs, but I finish them off with two top coats of Sikkens Cetol Marine Gloss. Confusion enters the scene when you talk about Cetol, because most people seem not to understand that it's really a two-part system.
I would say that Sikkens is remiss for not informing its customers, via the application information on the can, that if you're going for a straight Cetol job, it's best to use three coats of the base pigmented product (Cetol Marine Natural Teak) and to top it off with multiple coats of the clear gloss second part of the system.
Sikkens (a division of Akzo Nobel) will never tell you that the gloss version of Cetol can be applied over spar varnish, understandably, because of theoretical possible incompatibility problems, thus the disclaimers you'll read on the can.
Rebecca Wittman has wisely informed us that any products which use the same solvents in their formulation are compatible, and may safely be used in lieu of one another, in correct sequence. I've found this to be true in my experience, and now routinely top off all my varnish jobs with two coats of Cetol Gloss, which lasts longer and keeps its glossiness longer than any spar varnish on the market.
As I said previously, I build up eight to ten coats of Awlspar, and then finish with two coats of Cetol gloss. This twelve coat brightwork system will last a year before needing maintenance coats, even in the harsh solar conditions of South Florida.