Configuring a TLS SIP Trunk on Avaya CM6

it would only need to be the CM application that has the certificate loaded.

what issue are you seeing with TLS ? Have you reverted to TCP to isolate security?

1. I dont know about better as the two protocols do what they do , Sip obviously is the way forward and tls is encrypted at inception rather than a third source encryption so for me that is the way forward , it is also much easier to trouble shoot than H.323(in my opinion)

2.Again better or worst is a bit difficult , a direct sip trunk from cm to the cisco will work fine and you have two points of failure , Session manager would be what Avaya want you to deploy but it does add another point of failure and tbh if you dont have session manager its a lot to invest in for a simple set up , that said SM does provide you with a lot of manipulation and options ...so really you need to decide what functionality your estate needs to do now and where will it be in 2 years.

3.To get the link to the cisco working is pretty simple via sip if you are struggling post the config of your , trunk , sig , aar , route pattern , pri/pub table based on how you are routing.

see this link it connects to SM , but you basically configure the trunk the same and in the sig group you would have the cisco node name instead of SM.
APSS (SME)
ACSS (SME)
ACIS (UC)