When is a Utility Knife to be preferred over a Chef’s or a Paring knife

Both the Santoku and French knives will work for the same types of things, so a lot of it comes down to preference. Santoku knives are lighter, so this can lead to less hand strain and quicker cutting. One thing that the Santoku are very good at is very thin slicing of vegetables, for two reasons: first, as you point out, you do not use a rocking motion, but rather chop down in one motion, which with practice can be quicker and more efficient. Second, Santoku knives usually have a much thinner blade angle (around 15 degrees vs 30-40 degrees on a French knife). This is because one side of a Santoku is flat, and the other side is beveled (like a chisel), so you only sharpen one side. To accommodate this thin blade the Santoku knives will be made with a harder steel, which helps maintain blade sharpness, but may increase the propensity for chipping if misused, and also makes them harder to sharpen.

Still, personal preference dictates which knife to use. Many people prefer the Gyuto style of knife, which (roughly speaking) combines features of both Santoku knifes and French knives. They are made of a hardened steel, are sharpened on both sides, but maintain edges around 22-26 degrees. The Gyutos, like the Santokus are fairly light. Gyutos also have a rounded belly but it is less pronounced than on a French knife.

There is much more to be said, but basically the thing to do is get your hands on some knives and start experimenting--see what you like!

One of the most important things is a full tang. The tang is an extension of the metal of the blade into the handle. In knives with a full tang, it goes all the way through the handle. This improves stability, control, and durability. Cheaper knives with partial tangs will have the handle break off over time.

In a chef's knife, you want a blade from 8 to 10 inches long, whichever is more comfortable.

You can also either get a forged or stamped blade. I suggest reading this article on the differences. To summarize, forged blades are softer, easier to sharpen, heavier, and have a bolster. Stamped blades are sharper, harder to sharpen, lighter, and have a welded on a bolster if any. With current manufacturing processes forged is not necessarily better than stamped. You should make your own decisions. All crap knives are stamped, but not all stamped knives are crap.

This brings me to one of the most important points: It must feel good in your hand. Don't buy an expensive knife just because it's expensive, or you recognize the name. Go to a store that will let you use the knife, Williams-Sonoma will do this. If you can, bring a carrot in your pocket and actually cut that in the store.

_{I'll do some research on steel quality and update this later.}