It depends on if you mean, what do I look at first when I first see a particular light, or, what do I look for when looking FOR a light?
The question is so broad and open ended for me either way, that its like asking: "What is the first thing you look for in a tool?"
If I see A tool, I might consider what I might be able to use it for....given its attributes.
If I see that I need a tool, and am starting the search for one, its a search for a SET of criteria...that will result in a tool that does what I need it to.
For example, if I need a tool to screw in a torx bolt...the first thing I look for is if it CAN drive a torx bolt....and then I'd consider how well suited it was for the task, how long it might last, cost, etc.
If I am given a box of lights to use for a disaster recovery operation, I might sort through them and pick some to cover the long range aspects, some for close range, and some for mid range...and if the weather or sea conditions, etc, warrant it, the water resistance/usefulness/survivability in that scenario...the availability of power/spare cells for recharging vs runtime and so forth.
If I am SHOPPING for a light for the above scenario, I would be looking for a SET of criteria that would be analogous to looking for something to drive the torx bolt, etc.
So there is no one thing I look for FIRST really, as the FIRST thing is the niche it has to fit...and that dictates the light's desired attributes.
If I didn't USE the lights, and I just collected, say, throwers, then I'd look at cd first, or if I only liked warm tints, I'd look at it to be sure it had a warm tint first, and so forth.
If I USE the lights, then I might say, OK, the cool white will find the missing person first because its going to put more lux on target than the same form factor warm light...and it does me no good to know if little johnnies shirt was more navy or less navy if he's dead because it took too long to see him, etc.
If the range little johnny is at is adequately reached by a warm light, sure, there's even a chance his shirt will stand out from the rushes he's in better, or, maybe, that it will be even harder to see, depending on the shirt.
I might be better off with a light so far to the cool side its UV, so his shirt fluoresces and glows like a beacon....and so forth.
IE: What is perfect for some people is awful for others, and visa versa.