I have used both programs (WaterCad and KY Pipe). Setting up a system for analysis in WaterCad is pretty intuitive, and components of the system are easy to modify. The biggest drawback to WaterCad is that it is now sold by Bentley, and their licensing policies are pretty draconian (I am sure others would agree). WaterCad also has this funny quirk where it will satisfy a demand node, regardless of the fact that is has to create a -50,000,000 psi vacuum to do so. (Try it, it is pretty funny. If the pumps don't run, no problem! Just suck the water where you need it to go!)
KY Pipe works just fine as well, it takes some getting used to, and if you do have a problem, you can speak directly to someone who is willing to look at your file, work on it a while, then offer a solution. Price-wise, KY Pipe is the better bargain. You can download a 50-pipe demo for free from their website to give it a try.
I would recommend KY Pipe over WaterCad.