I am a monohull sailor (and not terribly experienced), but I have chartered two cats. I found maneuvering a cat to be much easier than a monohull. With two engines you can essentially spin a cat in place. The maneuverability advantage seemed to far out way the lack of visibility. (How well can you see the end of a 40 ft monohull anyway?) And on one of the charters we lost an engine in a narrow channel with a barge approaching. Sure was nice to be able to keep going while we figured out what was wrong.
I will agree with everyone else about the added comfort and space. As for sailing, one of the two sailed great. I missed the ability to feel what was going on, but it was fast and pointed well enough. The other was a completely different story. I am sure it was mostly my lack of experience, but I just couldn't get it to tack. And upwind was a jarring experience as it pounded into the waves.
I will still choose a monohull, but I wouldn't hesitate to charter a cat on occasion if the rest of the crew wanted one.