The Navy project I work with has a wide variety of modems from at least a
dozen different manufacturers.
 
With regards to async modems, the most reliable and flexible modems the Navy
has are the Multitech, followed by the US Robotics Courier modems.  The only
real difference in reliability that we have seen is in how the modems
survive phone line surges due to thunder storms.  We have NEVER lost a
Multitech modem due to a thunder storm.  There have been instances where
every non-Multitech modem at the site was fried by a thunder storm.  In five
years we have yet to have a single Multitech modem fail.
 
The one problem we have had with the Multitech modems was that 3 or 4 years
ago.  We found that we had to plug them in and leave them turned on for 24
hours before configuring them or they would lose their new configuration
(this is no-longer a problem with their newer modems).
 
The US Robotics Courier modems work very well also, but we have had a few
fry due to local thunder storms.
 
After the Multitech and Courier modems comes UDS.  These have often been a
pain to configure, but at least they don't die with EVERY thunder storm and
they don't die randomly.
 
At home I have a Cardinal 28.8 and have had good luck with it - except once.
A thunder storm killed it in June.  I called Cardinal and told them the
modem wouldn't dial out, they gave me an RMA, I mailed it to them, and 6
days later I got it back.  There was NO CHARGE for the repair, and there was
a nice letter saying that components x, y, and z had been replaced and that
that information would be applied to the design of their next modems.  Great
customer service. (I now have a Radio Shack phone line surge suppressor on
my home lines.)
 
Along the lines of if you can't say something nice, don't say anything, so I
won't comment on our experience with Boca, Zoom, GVC, Hayes, ...  or my
personal experience with Hayes.
 
Our mobile users favor the MHZ PCMCIA modems with the X-Jack.  I don't know
of anyone breaking the X-jack off, and the modem works like a champ.  I
bought one for my personal laptop and like it.  I have enjoyed having only
one cable to carry around - a standard 6 foot modular phone cable (which if
you forget it, you can easily replace at any Radio Shack, Home Depot, drug
store, Giant Food, Safeway...).
 
For our dial sync lines we like the Racal-Vadic 3222 (built by Penril I
believe).  They support a number of our fallback and "on demand" circuits
around the world.  For our dedicated circuits we generally use Codex modems.
Our DSUs are from various firms and all have been very reliable.
 
John Korb
Innovative Software Solutions, Inc.
 
The opinions expressed herein are solely those of the author.