What is better to use:
what are the pro's and cons... ?
DMotion is preferred. It captures all transactions while the migration is happening and has no downtime. It does not, however, upgrade the virtual hardware.
Converter will import with the original VM running, but any transactions occuring after the initial disk snapshot may be lost. Converter will also require a reboot of the VM to properly configure the virtual hardware and will involve a disruption of service. But it will also upgrade the virtual hardware for you.
Converter would be a good alternative if you have two different esx host platforms. I have to migrate between two different CPU families.
If you have 2 different CPU platforms, a hot migration isn't an option. At that point you might as well use VirtualCenter's cold migration.
Depends on what you are trying to accomplish I guess.
If you are moving Virtual Machines on ESX with virtual center to different storage or different hosts and have shared storage, then DMotion is best, no downtime. Even if you don't have shared storage, then I would use a migrate first before converter, less steps.
If you need physical machines, the converter is the obvious choice.
If you are moving Virtual Machines without using Virtual Center, or between different host platforms, then converter is the best choice, more flexibility.