given what jmo said, ie 'you can't put a value on human life' then you can't order (greater than and lesser than are ordering operators) these to things.
It is not a simple question to answer (or i guess you, steephie, wouldn't have asked it) but the asking implies that there is a simple answer, to which I say there is not.
There are many factors which complicate the issue, and living in a world where such things can be simplified may make you feel happier, but it is not the real world... (though you might argue that we all live in simplified models of the real world which our brains are capable of comprehending... ) anyway, making some simplifications can result in answers like : "Two suicides are obviously worse than one homicide."
A suicide could be seen as a good thing, particularly (in the entirely hypothetical) if it was on a mountain where you (and your family) had just crash landed and your body was needed as food for your family... (hence comments above about choice of the dying) but self-sacrifice is a general trend among lots of human, usually self-sacrifice does not require suicide - because we build social structures to support each other, whether economically, emotionally, educationally or whatever.
Suicide is thus a failure of those social supports, some suicides are a result of mental illness, though this is far from universal (i suspect) some people with terminal illness want to choose when and how they die, (dying with dignity) while others with non-terminal but chronic illnesses may also wish to 'end their misery'
Meanwhile homicide sucks, but as was pointed out, is sometimes legal - though the definition is a human killing another human, and I guessing that capital punishment
is seen as killing of a human by the state rather than by an individual... i'm going to go and include it, as the state is a collection of humans (though i find this to be a difficult question on it's own, especially as the whole is often greater than the sum of it's parts)
Regardless, in this case it is considered to be a good thing. Now which is worse, well i think that suicide to reduce suffering (when mental illness is not in question) is better than capital punishment to prevent potential suffering which the criminal has not yet committed. And while it may satisfy a need for vengeance, i think that the gain is smaller.