guess its a "which is cheaper" quesiton

Not necessarily. The cost of the extra wire and resistors required at 3v is extremely minimal especially when buying stuff in packs of 25 or 100 pieces. Going with 12v is just 8x AA batteries so in the end it doesn't actually cost extra because by the time you are replacing the 8 AA batteries in 12v, you will have replaced the two AA batteries in 3v four or five times.

It's more about where the leds are going, how many of them are going there, and how much space I have to work with, which is where 12v wins.

being compact does tend to win in companies because it reduces costs. i'm notably referring to those extra resistors and like you said, wires.

Yea having 8 AA batteries can add a buch of weigh where you store them at. Also I use rechargeable type AA batteries where I can only recharge 4 at a time. But LEDs are low power so 8 AA batteries should last virtually the whole convention when you are using it. But personally even though it takes more work and parts, I rather have it set to 3 volts or 2 AA batteries and recharge the batteries every night.

Here is why I'm using 12 volts, I made this newer diagram: https://www.dropbox.com/s/xtosth4nt.....plans.png?dl=0

As for storing the batteries, I will either put them in my belt clip camera bag or my pocket.

Who knows though, I might end up changing my plans around later. I want this thing to be visible in daylight. And I did a weird thing with multiple switches because I don't want to mess with stuff that generates heat like a potentiometer or voltage regulator. The resistors in a layout like this barely even get warm but they allow the leds to work across a wider range of voltages before they noticeably dim.