I've done Kindermusik and Kindergym with ds1. I personally like the kindermusik better as it had a mix of activity, music, quiet time, etc. (but I used to be a music teacher so am biased about all the fantastic benefits of music!) where I felt the gym was more just activity without the structure.

DS1 started kindermusik when he was 6 months and went for a year at which stage he started swimming lessons instead. I'm planning on doing the same thing with ds2. DS1 will go back to some sort of music lessons within the next couple of years too.