Dear Parallel Programmers,

I have used a little LAM/MPI few years (3/4 years) ago, and after that there is a big gap. Now, I am starting to use parallel programing again. For general case (distributed as well shared memory case), there is MPI. However, I have seen different variant of MPI like OpenMPI, LAM/MPI, MPICH2. What are differences among all theses: MPI, OpenMPI, LAM/MPI, MPICH2? Do you guys suggest for me the better one? I want to stick with one (and off-course open source) so that I do not have move from one to another.

Thanks.