Here in the U.S. (re: jno) the problem with a life sentence (other than life without the possibility of parole) is that many attorneys make a fairly good living appealing the sentence... often time years if not decades later. The criminal is most of indigent and the State pays for the attorney fees.
It need not be plain old ordinary murder that can result in a death penalty, but even so, for the layman it's often difficult to determine the difference between one killing and another, both of which recieved differing sentences.
As an aside, here, the individual State has its own set of statutes to determine death penalty or life in prison. A neighboring State (here in the west) is about to vote on adding a firing squad as an other accepted means of executing a criminal. The State of Utah has had such a means on the books for decades, but is, at its heart, religiously based to satisfy certain requirements for executing prisoners who may be Mormons. At any rate, the type of execution is the choice of the criminal...