I like the security of a “pass-through” watch strap — that is to say, a single piece that weaves through/under both spring bars. Such a strap provides the greatest security, since one of the spring bars can fail and the other will keep the watch on the strap (which remains buckled to one’s wrist). Both NATO or RAF/milspec straps are “pass-through” straps.
Maratac straps are my favorite pass-through straps. The fabric they use is outstanding: strong, comfortable, and quick drying. The hardware is what I would describe as milspec wire — true to the original UK Ministry of Defense (MoD) specifications. Other fashion NATOs, often the more expensive ones, use a buckle with a spring bar that can fail, not so with the milspec wire buckles. The risk may or may not be significant, but why introduce it? The straps are also “welded” much like the original UK MoD spec and the NATOs are stitched as well. I add a few stitches to the milspec type to mirror the “belt and suspenders” security of the NATOs. Prices are fantastic for the quality. Color choice and availability are the only drawbacks.
I prefer the milspec variant, since, with its single layer, one’s watch sits closer to the wrist. A watch can feel like its teetering on the two layers on a NATO strap. Having said that, it really depends on a few things, as I see it: your wrist, the watch caseback, the watch case size to lug width ratio, and lug shape. My Citizen Pro Diver (my only quartz watch) feels great with the Maratac NATO despite its 43mm diameter case and 20mm lug width. That’s because it has a flat caseback (which one often sees with quartz watches) and short lugs that hug the wrist. Additionally, the milspec straps have a cloth keeper, which wears more easily at a desk (when typing) and under shirt cuffs than does the NATO hardware.
I have not used the Maratac Zulu straps. I generally do not like Zulus due to heft of the thickness of the fabric or the hardware. Both are overkill and not comfortable for me. Two-piece straps allow one’s watch to sit flatter, of course. However, the security benefit is not there. If a spring bar fails, and you do not notice in time, your watch could hit the sidewalk, a bathroom tile floor, or worse (get lost in the surf at the beach, etc.).
On a final note, I have used the Marathon, official US Mil strap (given to me by a friend who is a member of the MA National Guard) and much prefer the Maratac milspec version. The Marathon version is longer, which would be a help when wearing one’s watch over a wetsuit, jacket, etc. The Marathon requires the end be doubled over in the keeper. The Maratac has an end that protrudes just past the keeper on my 7 1/4” wrist. The fabric is not as comfortable as that used in the Maratac version.
I buy Maratac straps at countycomm.com.