Which tyre additive

[Xracer]

I'm just wishing to clarify which additives work best on different tyre and track conditions, I have been using SXT 3.0 all of the time on the Contact GT12 tyres but I am aware that there are better options like Spider Green or Blue that appear to be favoured too, amongst others of course!

Any advice guys, especially for the various compound and hardness's of the JFT GT12 tyres and especially now we are using the softer grades which I have not tried yet?