Best Of Breed Batch Systems & Schedulers

[Dan Sturtevant]

I appologise if this has been addressed many times over (i'm sure it has 
in many forums).

I am trying to evaluate the current field of batch systems, schedulers, 
and technologies that tie multiple heterogeneous clusters together (grid).

I want to install and configure multiple configurations to test the 
functionality and ease of use of different systems, but need to know 
where the best prospects for success are before beginning.

My search is somewhat limited by the need to use open and freely available 
software components.

The two obvious batch system choices of which I am aware are Veridian's 
OpenPBS and the Sun Grid Engine.

On top of OpenPBS, there are multiple schedulers (Maui, UnderLord).

Grid schedulers include Silver and OverLord.

What are the most viable projects in this field based on current features 
AND the rate of development of patches, updates, and enhancements for 
each?

Where is the best place to begin building ground up if the goal is to 
create a full featured grid environment?  What are the relative strengths 
and weaknesses of each approach?

Thanks in advance for the advice,
Dan Sturtevant