No, GT and Mesa are not necessarily the "best" tubes. Again, they buy from the same manufacturers as everyone else and just have their own rating systems. A little googling will tell you which of their tubes come from where, I know in GT if the tube has a "R" on the end it is Russian, if it has a "C" it is Chinese, like 12AX7R or 12AX7C.
There are only 3 or 4(?) places that manufacture tubes left, JJs are made in Slovakia, Shuguang are Chinese, but there was a fire at their plant a few years ago and it has been closed, supposedly will be opening again soon. PSvane are a relatively new brand from China. Svetlana New Sensor Corp is in Russia and make Electro-Harmonix, Svetlana, "new" Tung-Sol, Gold Lion, and maybe "new" Mullard tubes (might want to check me on that).
Of course, Russian tubes may be harder to get now given current events although EH seems to be able to import their tubes.
Again, I came up with this info quickly off the top of my head and a quick google search, so please double check me.