Jhaelan:
Aye - I was trying not to talk about characters and more campaign themes - magic vs. psi vs. technology vs. pre-Rifts vs. monsters and horrors and dbees.
Hmmm... I think I'd least like a CS/tech-only game as I've done several of them.
On the others:
Escaping slaves: I'd vote for this one first. Good variety of options. Some liberties would be needed for tech people, like finding an armory, freedom fighters passing out some basic equipment or scavenging items from guards during prison break. Gives an opportunity for some unique/rare equipment (depending on who enslaved who) in exchange for not getting to pick starting equipment. Works out great if the captor is a 'collector' that gathers odd things (creatures, items, ect).
Mercenaries/monster hunters/bandits: Gives the wide variety of player options. A solid 2nd vote.
Strangers: This is pretty close to Merc/hunter/bandits, as long as the players agree before hand it's not a free for all at start. It DOES give the greatest variety of options as we could literally pull characters from anyplace (or anywhen).