There are (so far as we've seen) eight attributes to each gun, which are listed in the polls, and each attachment or modification to that gun changes those statistics.
http://www.brinkaddict.com/images/brink9weapons.jpg
Want a high ammo capacity? Sure. Just put a tommy gun magazine on. Oh, just one thing though, those are a bit hard to handle, so it'll take a while to reload.
Looking for something you can rip off its holster at a moment's notice? Go right ahead. Just take off all those pesky grips that would've made it more stable.
Need a hard-hitting rifle that's as close to OHK as you can get it? That's fine. But how many of those high-caliber shells can you really carry around?
Or maybe you want to hit something a mile away, every single time. Well, that barrel will take some of your stopping power away, but I'm sure it's worth it.
All of these are valid enough possibilities of the sacrifices we'll all be making. The same way real-world weapon designers need to make compromises.
So vote, tell us what is most important to you, what you couldn't care less about, and why you've made those choices.