I may have said it here before, but the copper one will accumulate a black tarnish on it fairly quickly, extremely quickly if you're using it as a utility knife. If you want a straight metal look I would go for the brass 100%. Although I got the blue titanium one (after I got the copper one) and I like it a lot more. The copper one only looks sleek for about half a day after I clean it, then it loses it's shine after minimal contact with your hands. The colored finish on the titanium one will scratch a little and pick up metal-ish scrapes if it is on a key-chain(with keys). But the scrapes rub off, it retains a nice look, and it has a better grip, so I prefer it to the copper one :)
ALSO: For cleaning the copper one, mix like a half cup of white vinegar and a tablespoon of salt in a bowl. Disassemble it so you have only the two copper halves. Brush the surfaces with an old toothbrush, nothing abrasive is needed. Brush it under the surface of the solution if possible. Sometimes some grime will get in the little grooves on the back or in the button slide. Just use a toothpick to scrape it out and a little brushing will get the rest off. When its nice and shiny, rinse it off with water and dry it completely before re-assembling it. Use the blade changing instructions in the pinned comment if you need any help taking it apart. There are some cheap copper polishes out there that would keep it looking nice for a while, but I haven't used them, so I'm not sure if it would effect mechanism or grip or anything.
I hope you guys find this useful!
Edit: I want to emphasize that this is a knife for right handed people, there's literally no comfortable or even safe way to use it in your left hand.