IMO, a solid core syn gut in the mains with Sensation in the crosses would last longer for most people. Most people break the mains first and a syn gut is more durable than a multi, especially Sensation.
Multi's are strings made up of often over 1000 individual strands twisted together and bonded, often with some form of polyurethane. A regular synthetic gut has a single string for a core, and 1 or 2 layers of a smaller diameter string wrapped around the center core string.