Some people find that one works more effectively than the other, so which is used is really up to the patient.
Humulin, more commonly called
Humulin NPH, and even more commonly called just NPH, is a long acting insulin. It is absorbed more slowly, and it's effects last longer, about 12 hours. Usually NPH is used in combination with one of the fast acting insulins. An alternative long acting insulin would be Lantus.