UDP Jitter operation is covered in the Orion VoIP Monitor module.
UDP Echo is more close to what would be transfered during a VoIP Call, however it is not possible to set the DSCP value. The ICMP Echo has this option. There is no real best choice between UDP Echo and ICMP Echo + DSCP value set.
So in a sentence, what could be a better choice to test VOIP QoS? I believe ICMP Echo with TOS setting can be a good choice.
BTW, what is the real difference between UDP and ICMP echo?
If DSCP is implemented on your network I would choose ICMP Echo with ToS as well.
If there is no DSCP prioritizing traffic on the target network, I would choose UDP Echo.
The difference seems to be simply in the protocol used: ICMP or UDP.
More information there: