It's hard to say which company is the best for term life since it often depends on the individual's situation and personal risk factors; such as, age, gender, health, lifestyle, if you smoke or not, etc.
However, for medically underwritten term life insurance policies American General, Genworth, and Prudential are some of the more popular carriers, as well as, Banner Life.
Another option for term life insurance you may want to consider is the no medical exam term life policies. Among the leaders providing these types of plans are National Life Group, Assurity, American National, and Sagicor, though you will pay rates about 10% higher (or more) for those policies.
Here is a list of the top 10 term life insurance companies which is issued each year from the III.org (Insurance Information Institute).