Transient voltage supression for high voltage Thyristor or Avalanche TVS

I am making a high voltage 240 VAC 60Hz voltage measurement front end and is in need of a transient suppression device. According the a table in wikipedia.

Avalanche and Thyristors are the only remaining options to choose from. Are there any other factors that i should consider aside from the one in the picture?

I am leaning to use the avalanche type because it is something that i am familiar with in low voltage applications, so choosing parts is not that difficult i already even have a tentative part from littlefuse and bournes. Thyristors on the other hand i am not familiar with the terms they are using.

Is it worth using a thyristor?

EDIT:

I have narrowed down a bit on the limits of what i want to protect, so far in my design process i have used 2000 V as my absolute maximum in term of component spacing, resistor selections, and isolation barrier. I tried to choose components beyond this where possible, but 2000V is where i draw the line. Also fits great for level 3 IEC/EN 61000-4-5 certification (im not going to certify this device)