If the characters are completely unlinked to each other, then the benefits of the greedy, evil choice are automatically null and void. The only reason to choose them is a latent desire for mayhem.
Good becomes the only real option because you at least leave the episode on the imaginary moral high ground.
More over, with little time to connect to characters, the personalities and motivations of a single players character pool are likely to be similar if not the exact same, meaning what happens in your first adventure or two will resonate through the rest of the campaign.
How about this...
If the characters are presented with a fairly black and white choice - overthrow a flourishing kingdom or save it, aid the scam artist or expose him - then give them set rewards that will transfer to later characters.
The evil choice, usually the easier and more profitable one, will grant the extra money or an magic item to the player's next character.
The good choice, usually the harder and less profitable one, gives a physical, statistical bonus above and beyond simple XP.
The result is an actual choice - if the player goes all evil, he'll have oodles and cash and magic items, but he'll be inexperienced, frail, and easily defeated. If the players goes all good, he'll be a mental and physical paragon in rags and impoverished.
This almost forces some sort of mid-road, in which characters dabble in a sort of gray area and the effects of their choices resonant not only in the world, but in themselves, regardless of changing characters.