I would choose them based on speed and overhead.  To date, the PWSCS
method is the fastest with the lowest overhead going to VM.  PWSCS is
a very nice product, but not pervasive across the industry.  If you have
it I'd use it.

Second would be TCP/IP.  It is a little slower in speed and higher in
overhead, but has the "industry standard" stamp of approval on it.

As a last resort there is the 3270 protocol.  You should steer away from
this for your 1gig systems since the 3270 protocol will never scale up
to meet the needs as your systems grow.  We (ADSM) support the 3270
protocols as the entry level protocol for those sites that still have a
large amount of legacy systems and haven't installed a highly connected
lan environment yet.

I hope this helps,

Paul Bradshaw