Fun question!

I guess in addition to preference and availability of materials, you could factor in: whether or not you have any other fire-starting choices; whether the current conditions make success with a given fire-starting method likely; whether you really need fire; and whether it makes sense to try to start fire where you are or to move to an area with better shelter, water, food, fire fuel, likely signaling success, or other survival pluses.

Edit: BYW fire from magnified sun can be done with a lens created from clear ice, a shined aluminum can bottom, some eye glass lenses, parabolic-shaped reflectors or reflector arrays, and probably a host of other ways of which I would be delighted to learn.