Which whole house dehumidifier?

Got a bi-level house near St. Louis, MO. The house has cinder block walls on lower level. Humidity level this spring on the lower level has been consistently running 80-90% with very musty smell. This is the first season I've actually monitored the humidity levels. I know I need to address this problem ASAP. Maybe it's just me but I don't feel very energetic when I spend much time breathing the air in my home in the spring and summer time. I try to spend most of my time on the upper level, but even then I sometimes smell the mustiness. I have a lot of sinus problems too. Anyway, I'm considering installing either an Ultra-Aire APD 100V or an Aprilaire Model 1700 to address my problem. In comparing these two are there any advantages or disadvantages of one over the other? I know they hookup differently to the duct system. Am I on the right track considering these units? Any input will be much appreciated.