Sega all the way, going by the time period instructed in the OP.
Xbox that came after that time period is acting more like a barrier towards Sega's real potential and comeback in todays console markets. It could potentially of been a "riches to rags back to riches" success story.
We would be having a Three way console POWER war between Nintendo, PlayStation, and SEGA if Xbox hadn't arrived in time preventing SEGA's return.