I am operating under the premise, if I understood it correctly, that we are dealing with six strangers about whom we know nothing. If we do nothing, five people will die. If we act, one person will die and five will be saved.
First off, if you divert the trolley from its natural course, you are not "letting the one die," you are murdering someone who otherwise would have lived. Granted you are attempting to save five others, but this does not take away from the fact. I am not trying to malign the action, just attempting to cast it in its proper light. And the mere fact that is is murder does not change the equation in any way. On the other hand, if you allow the trolley to continue on its course, you are letting those five die so that you do not have to murder the one. I suppose technically allowing the five to die could be considered murder as well, but I am not sure I would label it as such, unless the person choosing also released the trolley.
Saving the five basically boils down to a numbers game. If you subjectively concede that human life has value, and you believe for whatever reason that the more things of value there are the better, then it logically follows that the five should be spared at the expense of the one. Yet this line of reasoning is only logical if you accept that premise... and there is no objective reason to do so (unless you are for some reason collecting humans, or getting a commission for each one, hoping for more converts, etc.). More of anything is not inherently, objectively better.
According to my own subjective ethical system, I am not sure what I would do. I feel that human life (along with all other forms of life) has no inherent value, other than what is given it subjectively by individuals. That said, I have absolutely no desire to contribute to the destruction of life; quite the contrary, actually. My gut response is to save the five and kill the one (irrationally based on the numbers game to which I do not consciously subscribe). Then again I am also rather passive, and do not necessarily believe that more is better, so I am not naturally inclined to attempt to save five who are passively doomed by actively killing one person. And yet...I would in all likelihood kill the one and save the five in the heat of the moment. Give me time to reason it out, and who knows? I certainly wouldn't blame someone for choosing not to kill the one. Or for killing her/him for that matter.
Some other hypothetical permutations:
1. Would you want you and your four fellow passengers to be saved at the expense of this other person?
2. What if we replace the passengers with five puppies, but leave the solo player human? Does this change anything? Five kittens? Five chimps? The last five baby seals on the planet?