Hi Pilou,

Zbrush Decimation master is a good decimation tool,
but Balancer is more robust (no mesh artifacts, skinny triangles etc),
faster, needs much less resources and thus can work easily
with very large models, and can preserve more details given
the same triangle count. Also the latest version of Balancer
has a unique feature to simplify models down to your required
error tolerance. So, basically you get guaranteed visual appearance
without thorough inspection and adjustment of triangle count.

You may take a look at some comparison of
Zbrush Decimation master vs Balancer here:
http://forums.luxology.com/discussion/topic.aspx?id=40386

Here is a comment by a Balancer user on ZBrush:
http://forum.reallusion.com/Topic65513-85-2.aspx#bm105007