First of all, I think you're really going to enjoy whichever ZL headlamp you choose.
Beam Shape:
The H600 series has a reflector and clear glass, so it's most like a regular flashlight, with a definite bright center area (for distance viewing) and good spill for still seeing closeup.
The H600F series has a reflector too, but adds a lightly frosted glass in front, which smooths the beam a bit. It still has a brighter center, but not as pronounced as the H600 series.
The H604 series has no reflector, often called a "mule", this beam is pure flood, so no center hot spot, excellent for closeup, but not so good for distance.
I find the F series to be the best all-around beam shape, giving a nice even flood for closeup work, but still having a bit of a brighter center spot which makes it useful for walking around. The regular 600 series, with the clear glass, is also an excellent choice, as you can always put a piece of frosted tape over the glass to even out the beam if you want. I'd only purchase the 604 series if you wanted a strictly closeup light.
By the way, one other reason I like the F series, is that the current crop of LEDs, when used with a reflector, tend to have a somewhat obvious color shift within the beam, meaning the color can be a bit different between the center and the edges, and the slightly frosted glass helps smooth that out.
Beam Color:
Here you need to consider both the Kelvin rating (color temp) as well as the CRI rating.
Kelvin refers more to the tint of the beam:
5700KCool White: This is usually slightly on the blue side, which many folks prefer, as it can appear as clean white.
5000K Listed with a "d" after the number, so H600d. Still slightly cool, but can begin to look warm.
4500K Neutral White: Listed with a "w" after the number, so H600w. This is a bit warmer, and often gives better color outdoors.
4000K Warm White: Listed with a "c" after the number, so H600c. Definitely warm now, sometimes a bit yellow. Very good outdoors.
CRI refers to how well the light renders colors, with numbers from 100 (best) down to 80 (ok). Typically, the lower numbers mean it wont show RED as well.
Personally, I find the Kelvin number to be more important, as it tends to influence to the overall color of the beam, but once I get the right color, I also prefer a HIGH CRI light, as I feel it produces a higher quality light, so I tend toward either a HIGH CRI "d" or "c" light, but I do have several "w" lights that have an excellent beam color. It seems that 4500K color temperature hits a sweet spot, and even though it's not HIGH CRI, the light looks very nice.
Mainly, I'd stay away from the cool white lights unless you just prefer that tint.
So, I'd recommend the H600F in either the "d" (5000K High CRI), the "c" (4000K High CRI), or "w" (4500K, 80+ CRI).
Remember, if you purchase from ZL, you'll have 30 days to try it out, and if you find out the beam isn't right for you, or the tint is awful, you can exchange it for a different one, with the cost of shipping it back being your only extra expense.
Anyway, good luck with your purchase, and let us know how it works out : )
