I tend to use the high definition PD 290 second modes when conditions allow that’s almost five minutes to send a picture as against the 140 odd of Martin mode one , the picture size however is larger, and very near photograph quality if free from QRM
The sstv “tones “ from the computer definitely need attenuating before putting to your rig for transmission and you will need to ensure the rig accepts the signals and transmits them with minimum distortion ,This can be fairly difficult to achieve but is essential.
The control of RF break into the computer is another problem and the cure is usually to make sure the Microphone is electrically disconnected whilst sending sstv and to adequately screen all leads (keep em short also ) and use ferrite ring filters when and where needed
Currently I use a home built relay type switching interface to achieve isolation
In UK the commonest mode used is Martin one , but Scottie one and Scottie DX are used in USA a lot .
As mentioned the PD modes are a little special and are not available in all sstv software .