[Asterisk-Users] Best echo-free and trouble-free system?

[Barton Hodges]

We currently have a 15-phone system using Asterisk, a combination of
analog phones/Grandstream HandyTone-286 and Grandstream BT101s, and 4
X100Ps connected to analog lines.  The system works well except for
the occasional echo problem.  I have all the echo parameters
configured, removed all the extra incoming analog lines except to the
PBX, etc. following all the advice on the wiki and on the mailing
list.  I'm not positive if the echo is due to the analog lines, the
X100Ps, or the SIP devices.

A customer has expressed their interest in purchasing a system with 10
phones and 4 incoming lines.  I do not feel comfortable duplicating
the system that we are using.  We are willing to put up with a little
echo now and then, but the customer should have every right to expect
a flawless system without echo, especially if they're replacing an
existing proprietary PBX without an echo problem.

What is the best setup for ensuring an echo-free and trouble-free
system?

Digital lines instead of analog?
Analog phones connected to TDM400P cards instead of SIP devices?
Analog phones connected to a channel bank that is connected to a
T100P?
Expensive Cisco SIP phones instead of Grandstream HandyTone ATAs?