Scalpel knives are excellent. They make some with disposable/replaceable blades for game processing. What I don't like about them are they seem they might be difficult to clean, and the blades are disposable and a bit expensive, which means they're always sharp, but you'll need a good supply of them. Box cutter, or the knife type of box cutter where it flips open are good, but there's not a whole lot of knife cutting area to work with, it can be hard to get the knife across the chicken's neck without your hand in the way, and get a good cut. And again it's hard to clean. Also I have small hands, and I want a knife that isn't 6" long - that's just too much blade for my hand with the size of the chicken I'm dealing with.
While you're getting knives, get you at least one cut-proof glove, or a stainless steel mesh gauntlet like they use for cutting meat in the deli. When the knife is sharp enough to process chickens quickly and effectively, it will cut you just by touching you - you will not even feel the cut and you will be bleeding badly. And God help you if your hand or the chicken unexpectedly slips - serious injury is a probability. Non-slip handles are necessities for me.
My favorite skinning knife is below - something about the blade shape, thickness, and flexibility make it perfect for removing skin from chickens without puncturing anything I'd rather not, and it's easy to sharpen with one of the handheld sharpeners (I don't know how to old-school sharpen with a sharpening stone yet). Very easy to clean, which I do multiple times throughout the process. I absolutely love this knife! Such a good tool!
I have a number of other knives i use for the throat, they're not perfect, but aren't bad. One is specifically for sticking the chicken, which if you do correctly is supposed to cause instant death (which is appealing - I'm all about a quick painless end - check out a butchering manual for details). Any of these would work, you just have to keep them really really sharp, like sharpen them every 2 chickens or so.
This is the poultry sticker knife for sticking the chicken, and can be used on the throat.
The two smaller knives here work well for most tasks with chickens. I like the gut hook but it's hard to sharpen, the more rounded the blade the more useful and less likely it will puncture things it shouldn't on the chicken or on you. These are usually what I use on the throat, and I keep both of them sharp and ready each time in case one of them is unexpectedly dull, the other is ready to use right away.
A lot of knife selection also depends on your body mechanics. What feels good to one person might not work for another. I've found just by looking at a knife I can already tell if I might like it for a certain task. So I only purchase or try knives I like the look of, because I instinctively have an idea how they would work in my hand.