best use of an EMC SAN

Assuming we have 24 73G drives is it better to make one big metalun
and carve it up and let the SAN manage the where everything is, or is
it better to specify which spindles are where.

Currently we would require 3 separate disk arrays.

one for the main database, second one for WAL logs, third one we use
for the most active table.

Problem with dedicating the spindles to each array is that we end up
wasting space. Are the SAN's smart enough to do a better job if I
create one large metalun and cut it up ?

Dave