What would you use for a brand new cross platform GUI app, CPython or IronPython ?
What about
 - license / freedom
 - development
    - - doc
    - - editors
    - - tools
 - libraries
 - performances
 - portability  
What can you do best with one or the other ?
 - networking
 - database
 - GUI
 - system
 - multi threading / processing
if you like/need to use .net framework, use ironpython, else CPython it's your choice
(or you can try PyPy :))
CPython or IronPython?