The diabetes medications Lantus and Levemir are similar, in that they are both basal insulin. This means they are long acting and mimic the kind of insulin levels you would get from a healthy pancreas. Both are also insulin analogues - that is, their molecules are analogous to human insulin but they're engineered to be absorbed more slowly. Neither Lantus nor Levemir corrects blood sugar spikes, because both release insulin gradually. If you need fast-acting insulin, you'll be looking at different medication.
Whether Lantus or Levemir is better is a matter of some debate. Levemir is injected twice daily generally, while Lantus is a once-a-day medication. Sometimes, Lantus can sting where you inject it. Some studies suggest Levemir brings less variable blood glucose-lowering impacts than Lantus, according to Diabetes Health. Levemir may cause less weight gain than Lantus does - a conclusion based on a 2011 review of previous studies.
If you have problems with low blood sugar on NPH insulin at night, taking Lantus in the evening instead may be good for you. You may wish to discuss this option with your doctor.
It's also worth noting that your insurance may cover either Levemir or Lantus, but not both. In that case, the choice may be based on financial considerations.