In general I would say that it's a personal choice and a matter of which methods are available. There are no patterns that would generalize from personality type, location, life history, etc. that I'm aware of.
Quite often it just comes down to convenience. Here in Toronto (Canada) jumping in front of our subway trains is popular. There was also a favourite bridge that jumpers used until they put up a very expensive suicide barrier. There's probably a new favourite "suicide bridge" now, but there's no consensus on which one that is yet.
By the way, I am speaking as someone who has a PhD in Psychology, but this is not a topic I specialize in. I do find the topic interesting, however; and, in light of a recent close friend's suicide just a few weeks ago, I'm preparing a suicide information resource web site. I have the URL... http://suicide-survivalist.org , but you won't find anything there yet. The first phase will be to "park" the site with a few useful links, while I build the site itself.