Cat -vs- Mono ?
I tend to look at the pros and cons of both options.
1)DRAFT- With a multihull, you tend to have a much shallower draft and a deeper draft on a monohull, however, it also depends on the size of the boat you are considering and the type of keel if considering a monohull. Hake Yachts makes a 32ft model that has a 20 inch draft with the keel fully retracted.
2)WINDWARD PERFORMANCE- You generally tend to lose winward performance on a multihull due to the increased side slipping encountered without having a keel to hold a line through the water. This may add considerable time to long voyages. However, on most other points of sail, multihulls generally tend to fair slightly better.
3)STABILITY- If you are planning to do any serious offshore cruising, this is something to consider. While multihulls are more stable initially, in the event they do blow over, they act like turtles on their backs and are not self-righting. Monohulls on the other hand are designed to let the force of gravity on the keel maintain the upright position (with heavy side down).
I personally favor monohulls over cats or tris partially due to esthetics, but also several other factors such as finding a slip to fit a multihull into. There are several great articles in the achieve here. Good luck!