mpich vs. openmpi

[Pavel Jurus <jurus@cs.cas.cz>]

On Tuesday 23 of October 2007 04:22:08 Adam C Powell IV wrote:
> Because my packages petsc, hypre, parmetis are moving to OpenMPI, I no
> longer use, nor have a strong motivation for improving, my package
> mpich.

Hello,

as a long-time user of mpich I'm interested how does openmpi compare to 
mpich2. Are there any particular reason why to prefer one over the other? Are 
there any compatibility issues when switching from mpich2 to openmpi? I tried 
to search web but haven't found anything useful.

Thanks,
Pavel