I always get excited when people start system-based fantasy games, but then they always start at level one. As though the campaign is meant to last long enough for us to see the good stuff. Am I right?
I'd love to see a fantasy campaign that used some edition of the D&D rules (I suggest this route this because it's relatively common knowledge, and because it's relatively simple to explain to a newcomer), which starts at at least level ten. Preferably higher. The PCs would already be movers and shakers. If people want secondary characters, or some people prefer to be involved at a lower strata of power, a troupe of servants, agents, hangers-on, prisoners, henchmen, cronies, proteges, and hirelings of all sorts could also be included.
My personal preference would be 1E, 2E, or BECMI for simplicity, but 3E is tolerable and 4E does have an intriguing new set of tools in the new DMG...