LDL cholesterol has a causal relationship with cardiovascular disease risk and is the basic test. ApoB provides an additional picture of the actual number of harmful particles, especially useful at borderline values or high triglycerides. HbA1c maps the average blood sugar of the past two to three months and is the standard test for detecting prediabetes or type 2 diabetes.
Your LDL cholesterol tells you how many harmful fat particles are circulating in your blood, and that number is directly linked to the risk of cardiovascular disease. The higher it is, the greater the risk, and the relationship is causal, not merely a statistical pattern. What a "good" number looks like for you depends on your overall picture: blood pressure, smoking, diabetes and other factors carry equal weight. You can have this measured easily by your GP with a standard lipid blood test, which is usually covered by insurance.
If you also have high triglycerides, or your LDL is right on the borderline, ApoB provides a more complete picture. ApoB counts the actual number of harmful particles in your blood, and that is sometimes a better measure than LDL alone. It requires the same blood draw, is inexpensive, and is increasingly included in a standard lipid panel. Not a diagnosis, but an extra lens on the same risk.
If you also want to know how your blood sugar is doing, add an HbA1c to that blood draw. This test shows what your average blood sugar has been over the past two to three months, and is the standard way to detect prediabetes or type 2 diabetes. A normal result is reassuring. A slightly elevated result means there is still time to act. In cases of anaemia or kidney disease the result can sometimes be misleading, so be sure to mention that to your doctor.
Overview covering multiple factors (4 research records, 5 sources). The strength of evidence differs by component, read the answer for the nuance.