There are a number of different categories or types of insulins and you can
divide them up in different ways.  This leads to some confusion.

Human insulin is insulin which is identical to that found in people. It is
produced by genetically engineered E-coli or yeast.  Human insulin is
distinguished from animal source insulin, beef or pork.

Analog insulins are insulins that have been created and designed to have
certain attributes that affect their absorption rate.  They do not exist in
nature. Novolog and Humalog are absorbed more rapidly than Regular human
insulin.  Lantus is absorbed much more slowly than Regular human.

Insulin can be combined with different compounds in order to slow down the
rate at which it arrives in the blood stream.  Terminology varies but in
the US the compounded insulins are, in decreasing order of absorption, NPH,
Lente, and Ultralente.

The overall list, again in decreasing order, is Humalog/Novolog, Regular,
NPH, Lente, Ultralente, Lantus.  The two fastest and the slowest are
analogs.  Note this list does not include the animal versions, the
compounds of which tend to be more slowly absorbed than their human
counterparts, for simplicity.

In general,Humalog and Novolog are called rapid acting.  Regular human is
called fast acting.  NPH and Lente are called intermediate acting.  
Ultralente and Lantus are called long acting.

So much for the differences.  Which one is better depends on what job it is
selected to do and where the individual patient falls in the significant
range of absorption variability.  The number of different insulin regimens
is large and the question of which insulin is best doesn't make any sense
outside of a particular context.

When people say, "This insulin is best", they are often saying, "This
insulin works best for me".  We all have a strong tendency to over
generalize our own experience.

Charly Coughran
ccoughran@DELETE-TO-RESPOND-UCSD.EDU