Optimizing resource scheduling

Is there a good way to get efficient resource scheduling?
When playing with different "select" modes I got these results:

select mode   duration
--            168.8
minloaded     140.5
maxloaded     133.6
order         168.8
random        126.7
--------------------
manual        116.7

So it seems even the best automatic scheduling mode (random)
gives a duration that is about 10% longer than I get with
manual allocation. Is there way to improve automatic scheduling?

And will random mode always give the shortest duration?

Thanks in advance.

Wolfgang Denk