Is it better to imprint from the Central or the generator?

Generally speaking, it is better to imprint from the generator. Plasma is a broad-spectrum transmission device. You can put a nice clean frequency into a plasma tube, and what you get out is a Smorgasbord of harmonics from the tube. When you imprint frequencies into the water, generally, the idea is to put known frequencies into the water. If you are using your plasma, you are putting a whole lot of frequencies into the water. So it may or may not be what you want to do. So most people will use a coil or the Spooky2 Cold Laser to imprint frequencies.
However, Spooky2 Central is the most powerful tool you can use for very serious conditions, such as very serious cancers. If you are currently treating yourself with Spooky2 Central, it may be a wonderful idea to have a vial of water nearby, and treat that whilst treating yourself with the plasma tube, and then between sessions, you can drink that water.
Spooky2 is wonderful for experimentation, and we get a lot of feedback from people for ideas, so this may be an idea where you can treat yourself with plasma during one session and then you can also treat yourself between sessions with water that has been imprinted with exactly the same frequencies that you have applied.