These are what I consider to be the three most important guidelines to think about when looking for a new EDC knife.
1. Carry only what you can afford to replace. Knives get lost, stolen, or confiscated. Expect one of these things to happen at some point. Do not carry a knife that is either difficult to replace due to price or impossible to replace due to sentiment.
2. Make certain your selection is legal in your state, town, and locations you expect to be going to. Laws on knives are almost as complex, backwards, and convoluted as gun laws. Research now. An assisted opening knife is considered a common pocketknife in some states and a deadly concealed weapon in others. All it takes it one accidental felony to ruin your life.
3. Carry only what you have the skill and/or the equipment to keep sharp and otherwise maintained. Some modern steels are very hard and difficult to sharpen. Also some blades are sharped oddly. Serrations are difficult to sharpen. All of these factors may require you to have more than a simple whetstone. If you are not used to sharpening knives, you may want to stick to more basic and easily sharpened steels such as AUS-8 and 440C until you have developed those skills. Also, look for simple blade shapes and avoid recurves and other more fantastic styles.