My Neutron Axis fly a little more stable than my ESP Buzzz and even more so that my FR Fugitive (now sold). I cannot comment on other plastic though, Neutron is all I got...
FWIW, I also threw I fugitive for a little while, and it wasn't as stable as a Buzzz if memory serves me right. It flew more like a MVP Tangent I believe... I now have a Tangent, and it feels really good in the end (flatter than a fugitive) and can be used as a laser approach disc.