ive done both. It probably depends on the teacher and your area but i would shell out the bucks for music together.
Kindermusic is cute. Yeah you get a little book and a cd and even a toy musical instrument and its cute. The ages are split which is that matters to you is good i guess. That is why i did kinder after music together. DD was not even 1 yet andi was told at music together after doing the baby class i have to move on to the 0 -4 class. She is tiny only 15 lbs now at almost a year and ijust couldnt see her getting along with big 4 year olds running around crazy.
I am doing music together for the summer. Its much less of an investment cause its only 4 classes.
In our kindermusic, the teacher was great, had a great voice etc. But she did not play an instrument, almost all the music was recorded and she did basically the same thingi n the same order each class. Also not a whole lot of actual musical learning going on.
At music together the teachers are required to play an instrument and sing live and they teach a lot mostly to the parents but the kids pick up on it. The materials used where more natural if that matter to you as well, to me it does. Like the silks used at music together are made of silk like sarah's silks and at kinder they are made of polyester as an example.
It really depends on the particular teacher i thinka nd also students in the class.
If I were you I would do music together for the summer, since it's cheaper foronly 4 classes then do kindermusic for the fall and decide which you like better.