I think that it really depends on what you are trying to do. For example, around the buoys racing would be better in a sloop. Whereas long tradewind passages with lots of reaching is great in a ketch. In my opinion, they are no harder to handle than a sloop (and actually do provide some extra maneuverability) even when single handing. However, it does take a bit longer to get underway. It is also more costly since the number of sails, standing rigging, running rigging etc increases. For larger boats and people who don't like powered winches, they make a lot of sense but boats smaller than 40' or so, I don't see this as a major advantage.
One of the biggest benefits in my mind is the ability to balance the boat with the sail plan. Almost all of the ketches that I have sailed have not needed an autopilot when reaching as their sailplan and rudder can be balanced well enough. Sometimes this means that one of the sails is not drawing optimally or that you need to reef one a bit early but it really does work quite well.
I happen to really like ketch rigs but if I were only daysailing or racing to windward a lot, I would pick a sloop.